WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

Class	Cusip	Orig Prin Bal	Begin Prin Bal	Int Rate Accrued	Int Rate Paid	Int Dist	Prin Dist	Int Shortfall	PPIS	Uncomp Int Shortfall	Prin Loss	Deferred Interest	Int Reimbursed	Unsched Int	Prin Reimbursed	Subsequent Recoveries	Total Dist	Ending Class Bal
A1	92922FZE1	$200,000,000.00	$200,000,000.00	2.3400000000%	2.3400000000%	$390,000.00	$1,554,461.68	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$1,944,461.68	$198,445,538.32
A2A	92922FZF8	$850,000,000.00	$850,000,000.00	2.3300000000%	2.3300000000%	$1,650,416.67	$6,606,462.14	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$8,256,878.80	$843,393,537.86
A2B	92922FZV3	$150,000,000.00	$150,000,000.00	2.4000000000%	2.4000000000%	$300,000.00	$1,165,846.26	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$1,465,846.26	$148,834,153.74
A3	92922FZG6	$276,500,000.00	$276,500,000.00	2.2000000000%	2.2000000000%	$506,916.67	$3,087,505.81	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$3,594,422.47	$273,412,494.19
A4A	92922FZH4	$50,000,000.00	$50,000,000.00	2.1900000000%	2.1900000000%	$91,250.00	$558,319.31	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$649,569.31	$49,441,680.69
A4B	92922FZJ0	$9,000,000.00	$9,000,000.00	2.2600000000%	2.2600000000%	$16,950.00	$100,497.48	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$117,447.48	$8,899,502.52
A5	92922FZK7	$146,509,000.00	$146,509,000.00	2.4300000000%	2.4300000000%	$296,680.73	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$296,680.73	$146,509,000.00
X	92922FZL5	$0.00	$0.00	0.0000000000%	0.0000000000%	$1,965,905.25	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$1,965,905.25	$0.00
X_NOTIONAL	XXXXXXXXX	$1,784,625,919.00	$1,784,625,919.00	1.3218940003%	1.3218940003%	$1,965,905.25	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$1,965,905.25	$1,771,547,600.43
X_PRINCIPAL	XXXXXXXXX	$0.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
B1	92922FZN1	$41,046,000.00	$41,046,000.00	2.5900000000%	2.5900000000%	$85,637.92	$2,050.67	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$87,688.58	$41,043,949.33
B2	92922FZP6	$20,523,000.00	$20,523,000.00	2.9900000000%	2.9900000000%	$49,431.93	$1,025.33	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$50,457.26	$20,521,974.67
B3	92922FZQ4	$12,492,000.00	$12,492,000.00	3.0400000000%	3.0400000000%	$30,591.52	$624.10	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$31,215.62	$12,491,375.90
B4	92922FZS0	$9,815,000.00	$9,815,000.00	3.0400000000%	3.0400000000%	$24,035.84	$490.36	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$24,526.20	$9,814,509.64
B5	92922FZT8	$12,492,000.00	$12,492,000.00	3.0400000000%	3.0400000000%	$30,591.52	$624.10	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$31,215.62	$12,491,375.90
B6	92922FZU5	$6,248,819.86	$6,248,819.86	3.0400000000%	3.0400000000%	$15,302.67	$312.07	$0.00	$0.00	$0.00	$0.12	$0.00	$0.00	$0.00	$0.00	$0.00	$15,614.73	$6,248,507.67
Y	XXXXXXXXX	$0.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
R	92922FZR2	$100.00	$100.00	3.6670000000%	3.6670000000%	$0.30	$100.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$100.30	$0.00
R_SYN	XXXXXXXXX	$0.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
YIELD_PAYMENTS	XXXXXXXXX	$0.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
Total		$1,784,625,919.86	$1,784,625,919.86			$5,453,710.99	$13,078,319.31	$0.00	$0.00	$0.00	$0.12	$0.00	$0.00	$0.00	$0.00	$0.00	$18,532,030.30	$1,771,547,600.43

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

Class	Orig Face	Beg Bal	Prin Loss	Prin Reimbursed	Subsequent Recoveries	Deferred Interest	Total Prin	End Cert Pct	End Cert Bal
A1	$200,000,000.00	$200,000,000.00	$0.00	$0.00	$0.00	$0.00	$1,554,461.68	0.9922276916	$198,445,538.32
A2A	$850,000,000.00	$850,000,000.00	$0.00	$0.00	$0.00	$0.00	$6,606,462.14	0.9922276916	$843,393,537.86
A2B	$150,000,000.00	$150,000,000.00	$0.00	$0.00	$0.00	$0.00	$1,165,846.26	0.9922276916	$148,834,153.74
A3	$276,500,000.00	$276,500,000.00	$0.00	$0.00	$0.00	$0.00	$3,087,505.81	0.9888336137	$273,412,494.19
A4A	$50,000,000.00	$50,000,000.00	$0.00	$0.00	$0.00	$0.00	$558,319.31	0.9888336138	$49,441,680.69
A4B	$9,000,000.00	$9,000,000.00	$0.00	$0.00	$0.00	$0.00	$100,497.48	0.9888336133	$8,899,502.52
A5	$146,509,000.00	$146,509,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	1.0000000000	$146,509,000.00
X	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
X_NOTIONAL	$1,784,625,919.00	$1,784,625,919.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.9926716751	$1,771,547,600.43
X_PRINCIPAL	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
B1	$41,046,000.00	$41,046,000.00	$0.00	$0.00	$0.00	$0.00	$2,050.67	0.9999500397	$41,043,949.33
B2	$20,523,000.00	$20,523,000.00	$0.00	$0.00	$0.00	$0.00	$1,025.33	0.9999500400	$20,521,974.67
B3	$12,492,000.00	$12,492,000.00	$0.00	$0.00	$0.00	$0.00	$624.10	0.9999500400	$12,491,375.90
B4	$9,815,000.00	$9,815,000.00	$0.00	$0.00	$0.00	$0.00	$490.36	0.9999500397	$9,814,509.64
B5	$12,492,000.00	$12,492,000.00	$0.00	$0.00	$0.00	$0.00	$624.10	0.9999500400	$12,491,375.90
B6	$6,248,819.86	$6,248,819.86	$0.12	$0.00	$0.00	$0.00	$312.07	0.9999500402	$6,248,507.67
Y	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
R	$100.00	$100.00	$0.00	$0.00	$0.00	$0.00	$100.00	0.0000000000	$0.00
R_SYN	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
YIELD_PAYMENTS	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
Total	$1,784,625,919.86	$1,784,625,919.86	$0.12	$0.00	$0.00	$0.00	$13,078,319.31	0.9926716746	$1,771,547,600.43

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004
PER $1000 DENOMINATION
Class	Orig Face	Beg Bal	Prin Loss	Prin Reimbursed	Subsequent Recoveries	Deferred Interest	Total Prin	End Cert Pct	End Cert Bal
A1	$200,000,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	7.77230840	0.9922276916	992.22769160
A2A	$850,000,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	7.77230840	0.9922276916	992.22769160
A2B	$150,000,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	7.77230840	0.9922276916	992.22769160
A3	$276,500,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	11.16638629	0.9888336137	988.83361371
A4A	$50,000,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	11.16638620	0.9888336138	988.83361380
A4B	$9,000,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	11.16638667	0.9888336133	988.83361333
A5	$146,509,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.0000000000	1,000.00000000
X	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
X_NOTIONAL	$1,784,625,919.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.9926716751	992.67167509
X_PRINCIPAL	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
B1	$41,046,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.04996029	0.9999500397	999.95003971
B2	$20,523,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.04996004	0.9999500400	999.95003996
B3	$12,492,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.04995997	0.9999500400	999.95004003
B4	$9,815,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.04996026	0.9999500397	999.95003974
B5	$12,492,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.04995997	0.9999500400	999.95004003
B6	$6,248,819.86	1,000.00000000	0.00001920	0.00000000	0.00000000	0.00000000	0.04994063	0.9999500402	999.95004017
Y	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
R	$100.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1000.00000000	0.0000000000	0.00000000
R_SYN	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
YIELD_PAYMENTS	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

Class	Orig Face	Int Rate Accrued	Int Rate Paid	Beg Cert Prin/Not Bal	Current Int Accrued	Int Shortfall	PPIS	Uncompensated Int Shortfall	Unscheduled Int	Int Reimbursed	Total Int Dist
A1	$200,000,000.00	2.3400000000%	2.3400000000%	$200,000,000.00	$390,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	$390,000.00
A2A	$850,000,000.00	2.3300000000%	2.3300000000%	$850,000,000.00	$1,650,416.67	$0.00	$0.00	$0.00	$0.00	$0.00	$1,650,416.67
A2B	$150,000,000.00	2.4000000000%	2.4000000000%	$150,000,000.00	$300,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	$300,000.00
A3	$276,500,000.00	2.2000000000%	2.2000000000%	$276,500,000.00	$506,916.67	$0.00	$0.00	$0.00	$0.00	$0.00	$506,916.67
A4A	$50,000,000.00	2.1900000000%	2.1900000000%	$50,000,000.00	$91,250.00	$0.00	$0.00	$0.00	$0.00	$0.00	$91,250.00
A4B	$9,000,000.00	2.2600000000%	2.2600000000%	$9,000,000.00	$16,950.00	$0.00	$0.00	$0.00	$0.00	$0.00	$16,950.00
A5	$146,509,000.00	2.4300000000%	2.4300000000%	$146,509,000.00	$296,680.73	$0.00	$0.00	$0.00	$0.00	$0.00	$296,680.73
X	$0.00	0.0000000000%	0.0000000000%	$0.00	$1,965,905.25	$0.00	$0.00	$0.00	$0.00	$0.00	$1,965,905.25
X_NOTIONAL	$1,784,625,919.00	1.3218940003%	1.3218940003%	$1,784,625,919.00	$1,965,905.25	$0.00	$0.00	$0.00	$0.00	$0.00	$1,965,905.25
X_PRINCIPAL	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
B1	$41,046,000.00	2.5900000000%	2.5900000000%	$41,046,000.00	$85,637.92	$0.00	$0.00	$0.00	$0.00	$0.00	$85,637.92
B2	$20,523,000.00	2.9900000000%	2.9900000000%	$20,523,000.00	$49,431.93	$0.00	$0.00	$0.00	$0.00	$0.00	$49,431.93
B3	$12,492,000.00	3.0400000000%	3.0400000000%	$12,492,000.00	$30,591.52	$0.00	$0.00	$0.00	$0.00	$0.00	$30,591.52
B4	$9,815,000.00	3.0400000000%	3.0400000000%	$9,815,000.00	$24,035.84	$0.00	$0.00	$0.00	$0.00	$0.00	$24,035.84
B5	$12,492,000.00	3.0400000000%	3.0400000000%	$12,492,000.00	$30,591.52	$0.00	$0.00	$0.00	$0.00	$0.00	$30,591.52
B6	$6,248,819.86	3.0400000000%	3.0400000000%	$6,248,819.86	$15,302.67	$0.00	$0.00	$0.00	$0.00	$0.00	$15,302.67
Y	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
R	$100.00	3.6670000000%	3.6670000000%	$100.00	$0.30	$0.00	$0.00	$0.00	$0.00	$0.00	$0.30
R_SYN	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
YIELD_PAYMENTS	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
Total	$1,784,625,919.86			$1,784,625,919.86	$5,453,710.99	$0.00	$0.00	$0.00	$0.00	$0.00	$5,453,710.99

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004
PER $1000 DENOMINATION
Class	Orig Face	Int Rate Accrued	Int Rate Paid	Beg Cert Prin/Not Bal	Curent Int Accrued	Int Shortfall	PPIS	Uncompensated Int Shortfall	Unscheduled Int	Int Reimbursed	Total Int Dist
A1	$200,000,000.00	2.3400000000%	2.3400000000%	1,000.00000000	1.95000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.95000000
A2A	$850,000,000.00	2.3300000000%	2.3300000000%	1,000.00000000	1.94166667	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.94166667
A2B	$150,000,000.00	2.4000000000%	2.4000000000%	1,000.00000000	2.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.00000000
A3	$276,500,000.00	2.2000000000%	2.2000000000%	1,000.00000000	1.83333335	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.83333335
A4A	$50,000,000.00	2.1900000000%	2.1900000000%	1,000.00000000	1.82500000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.82500000
A4B	$9,000,000.00	2.2600000000%	2.2600000000%	1,000.00000000	1.88333333	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.88333333
A5	$146,509,000.00	2.4300000000%	2.4300000000%	1,000.00000000	2.02500003	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.02500003
X	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
X_NOTIONAL	$1,784,625,919.00	1.3218940003%	1.3218940003%	1,000.00000000	1.10157834	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.10157834
X_PRINCIPAL	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
B1	$41,046,000.00	2.5900000000%	2.5900000000%	1,000.00000000	2.08638893	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.08638893
B2	$20,523,000.00	2.9900000000%	2.9900000000%	1,000.00000000	2.40861131	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.40861131
B3	$12,492,000.00	3.0400000000%	3.0400000000%	1,000.00000000	2.44888889	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.44888889
B4	$9,815,000.00	3.0400000000%	3.0400000000%	1,000.00000000	2.44888844	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.44888844
B5	$12,492,000.00	3.0400000000%	3.0400000000%	1,000.00000000	2.44888889	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.44888889
B6	$6,248,819.86	3.0400000000%	3.0400000000%	1,000.00000000	2.44888961	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.44888961
Y	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
R	$100.00	3.6670000000%	3.6670000000%	1,000.00000000	3.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.00000000
R_SYN	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
YIELD_PAYMENTS	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
11/2004 DISTRIBUTION REPORT
SERIES: WAMU 04AR12
WEIGHTED AVERAGE PC RATE: 3.66713%
WEIGHTED AVERAGE MATURITY: 362.11177
WEIGHTED AVERAGE LOAN AGE: 3.80549
POOL NUMBER: 2589
ISSUE DATE: 10/26/2004
CERTIFICATE BALANCE AT ISSUE: $1,784,625,919.86
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
BALANCES FROM LAST FISCAL MONTH-END:	3478		$1,784,625,919.86
PRINCIPAL POOL COLLECTION(S):
Scheduled Principal Collection Due Current Month		($128,370.31)
Unscheduled Principal Collection/Reversals		$1,451,918.80
Liquidations-in-full	23	$11,754,770.94
Subsequent Recoveries		$0.00
Net principal Distributed		$13,078,319.43	-$13,078,319.43

CAPITAL LOSS (PRINCIPAL WRITTEN OFF):			$0.00

BALANCE CURRENT FISCAL MONTH-END:	3455		$1,771,547,600.43

SCHEDULED INTEREST AT MORTGAGE RATE:		$6,085,765.89

UNSCHEDULED INTEREST AT MORTGAGE RATE:
Unscheduled Interest Collection/Reversals		$0.00
Interest Uncollected on Liquidation		$0.00
Interest Uncollected on Non-Earning Assets		$0.00
Interest Uncollected on Prepayment		$0.00
Uncompensated Uncollected Interest		$0.00
Net Unscheduled Interest Distributed		$0.00

OTHER:
Loan Conversion Fees		$0.00
Expense Reimbursements		$0.00
Gain on Liquidations		$0.00
Hazard Insurance Premium Refunds		$0.00
Recoveries Carried Forward		$0.00
Net Other Distributions		$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
11/2004 DISTRIBUTION REPORT
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
SCHEDULED SERVICING FEE EXPENSES:		$632,055.02

UNSCHEDULED SERVICING FEES:
Unscheduled Service Fee Collections/Reversals		$0.00
Servicing Fees Uncollected on Liquidation		$0.00
Servicing Fees Uncollected/Non-Earning Assets		$0.00
Net Unscheduled Service Fees Distributed		$0.00

MISCELLANEOUS EXPENSES:		$0.00

NET FUNDS DISTRIBUTED:		$18,532,030.30

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
11/2004 DISTRIBUTION REPORT
SERIES: WAMU 04AR12
WEIGHTED AVERAGE PC RATE: 3.66713%
WEIGHTED AVERAGE MATURITY: 362.11177
WEIGHTED AVERAGE LOAN AGE: 3.80549
POOL NUMBER: ALL
ISSUE DATE: 10/26/2004
CERTIFICATE BALANCE AT ISSUE: $1,784,625,919.86
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
BALANCES FROM LAST FISCAL MONTH-END:	3478		$1,784,625,919.86
PRINCIPAL POOL COLLECTION(S):
Scheduled Principal Collection Due Current Month		($128,370.31)
Unscheduled Principal Collection/Reversals		$1,451,918.80
Liquidations-in-full	23	$11,754,770.94
Subsequent Recoveries		$0.00
Net principal Distributed		$13,078,319.43	-$13,078,319.43

CAPITAL LOSS (PRINCIPAL WRITTEN OFF):			$0.00

BALANCE CURRENT FISCAL MONTH-END:	3455		$1,771,547,600.43

SCHEDULED INTEREST AT MORTGAGE RATE:		$6,085,765.89

UNSCHEDULED INTEREST AT MORTGAGE RATE:
Unscheduled Interest Collection/Reversals		$0.00
Interest Uncollected on Liquidation		$0.00
Interest Uncollected on Non-Earning Assets		$0.00
Interest Uncollected on Prepayment		$0.00
Uncompensated Uncollected Interest		$0.00
Net Unscheduled Interest Distributed		$0.00

OTHER:
Loan Conversion Fees		$0.00
Expense Reimbursements		$0.00
Gain on Liquidations		$0.00
Hazard Insurance Premium Refunds		$0.00
Recoveries Carried Forward		$0.00
Net Other Distributions		$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
11/2004 DISTRIBUTION REPORT
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
SCHEDULED SERVICING FEE EXPENSES:		$632,055.02

UNSCHEDULED SERVICING FEES:
Unscheduled Service Fee Collections/Reversals		$0.00
Servicing Fees Uncollected on Liquidation		$0.00
Servicing Fees Uncollected/Non-Earning Assets		$0.00
Net Unscheduled Service Fees Distributed		$0.00

MISCELLANEOUS EXPENSES:		$0.00

NET FUNDS DISTRIBUTED:		$18,532,030.30

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

Distribution by Group
Pool ID		Principal		Interest		Total
Pool - 2589		$13,078,319.43		$5,453,710.87		$18,532,030.30
Aggregate		$13,078,319.43		$5,453,710.87		$18,532,030.30

Number of Loans and Aggregate Principal Balance By Group
Pool ID	Beg Bal	Beg Count	Paid Off / Liq Count	Rem Count	Sched Prin End Bal	Sched Prin	Prin PrePay / Liq	Unsched Prin / Rev	Total Prin
Pool - 2589	$1,784,625,919.86	3478	23	3455	$1,771,547,600.43	($128,370.31)	$11,754,770.94	$1,451,918.80	$13,078,319.43
Aggregate	$1,784,625,919.86	3478	23	3455	$1,771,547,600.43	($128,370.31)	$11,754,770.94	$1,451,918.80	$13,078,319.43

Delinquency Information by Group
Pool ID	1 Month Count	Sched End Balance	2 Months Count	Sched End Balance	3 Months Count	Sched End Balance	4 Months Count	Sched End Balance
Pool - 2589	3	$1,829,559.43	0	$0.00	0	$0.00	0	$0.00
Aggregate	3	$1,829,559.43	0	$0.00	0	$0.00	0	$0.00

Foreclosure and REO Information by Group
Pool ID		Foreclosure Count		Sched End Balance		REO Count		Sched End Balance
Pool - 2589		0		$0.00		0		$0.00
Aggregate		0		$0.00		0		$0.00

Aggregate Loss Amounts by Group
Pool ID			Count			Loss Amount
Pool - 2589			0			$0.00
Aggregate			0			$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

INSURANCE RESERVES - Group 1
Insurance Type	Original Balance	Claims In Progress	Claims Paid	Coverage Adjustments	Coverage Remaining
MPI	$0.00	$0.00	$0.00	$0.00	$0.00
Special Hazard	$0.00	$0.00	$0.00	$0.00	$0.00
Bankruptcy Bond
Single-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Multi-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Mortgage Repurchase	$0.00	$0.00	$0.00	$0.00	$0.00

INSURANCE RESERVES - Aggregate
Insurance Type	Original Balance	Claims In Progress	Claims Paid	Coverage Adjustments	Coverage Remaining
MPI	$0.00	$0.00	$0.00	$0.00	$0.00
Special Hazard	$0.00	$0.00	$0.00	$0.00	$0.00
Bankruptcy Bond
Single-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Multi-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Mortgage Repurchase	$0.00	$0.00	$0.00	$0.00	$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.04AR12
Distribution Date: 11/26/2004

The Subordinate Certificates provide, to the limited extent described in the Prospectus Supplement, credit support, as well as special hazard, bankruptcy, and fraud coverage to certain Certificates. The "Prospectus Supplement" is that certain Prospectus Supplement, dated October 22,2004 to that certain Prospectus Supplement, dated February 10,2004, to which certain certificates were offered. The special hazard, bankruptcy, and Fraud coverage (collectively, "Credit Enhancements") provided by the Subordinate certificates provide coverage to the Loans, subject to the conditions and limitations to payment specified thereunder.



The Class Principal Balances of each Class of the Class B1,B2,B3,B4,B5,B6 Certificatesimmediately after the principal and interest distribution on 200411 are as follows:

Class			Class Principal Balance
B1			$41,043,949.33
B2			$20,521,974.67
B3			$12,491,375.90
B4			$9,814,509.64
B5			$12,491,375.90
B6			$6,248,507.67
Total			$102,611,693.11
Capitalized items used but not defined herein have the meanings ascribed to them in the Prospectus Supplement.
The amount of the special hazard coverage, bankruptcy coverage, and fraud coverage, as of the above referenced distribution date, is $0.00, $0.00, $0.00 respectively, and such coverages are referred to in the table above under the column "Insurance Type" as "special hazard," "bankruptcy bond," and "mortgage repurchase," respectively. However, no policy of insurance exists for any such coverage, notwithstanding the reference to "insurance."

WaMu Mortgage Pass-Through Certificates, Series 2004-AR12 8-K/A