


                                       UNITED STATES
                             SECURITIES AND EXCHANGE COMMISSION
                                   Washington, D.C. 20549

                                          FORM 8-K

                                       CURRENT REPORT
                             Pursuant to Section 13 OR 15(d) of
                            The Securities Exchange Act of 1934

            Date of Report (Date of earliest event reported) September 29, 2004


                   CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.,
                                      on behalf of the
          Adjustable Rate Mortgage-Backed Pass-Through Certificates, Series 2004-1
                   (Exact name of registrant as specified in its charter)

         Delaware                   333-107055-36                   13-3320910
----------------------------  --------------------------   ------------------------------
      (State or other         (Commission File Number)             (IRS Employer
      jurisdiction of                                           Identification No.)
      incorporation)

 Eleven Madison Avenue, New York, NY                      10010
--------------------------------------    ---------------------------------------
   (Address of principal executive                      (Zip Code)
               office)

Registrant's telephone number, including area code  (212) 325-2000.

                                    N/A                                      
                   (Former name or address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously
satisfy the filing obligation of the registrant under any of the following provisions (see
General Instruction A.2. below):

[  ] Written communication pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

[  ] Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

[  ] Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17
CFR 240.14d-2(b))

[  ] Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17
CFR 240.13e-4(c))

Information to be Included in the Report

Section 8 - Other Events.

ITEM 8.01. Other Events.

On September 29, 2004, Credit Suisse First Boston Mortgage Securities Corp. caused the
issuance and sale of the Adjustable Rate Mortgage-Backed Pass-Through Certificates, Series
2004-1, pursuant to a Pooling and Servicing Agreement dated as of September 1, 2004, among
Credit Suisse First Boston Mortgage Securities Corp., as depositor, DLJ Mortgage Capital,
Inc., as seller, Washington Mutual Mortgage Securities Corp, as seller and servicer, Select
Portfolio Servicing, Inc., as servicer, GreenPoint Mortgage Funding, Inc., as servicer,
Wells Fargo Bank, N.A., as trust administrator, master servicer, servicer and back-up
servicer and U.S. Bank National Association, as trustee.

Section 9 - Financial Statements and Exhibits

ITEM 9.01 (c). Exhibits.

(c) Exhibits (executed copies): The following execution copies of Exhibits to the Form
S-3 Registration Statement of the Registrant are hereby filed:

10.1 Pooling and Servicing Agreement dated as of September 1, 2004, among Credit
Suisse First Boston Mortgage Securities Corp., as depositor, DLJ Mortgage
Capital, Inc., as seller, Washington Mutual Mortgage Securities Corp, as seller
and servicer, Select Portfolio Servicing, Inc., as servicer, GreenPoint
Mortgage Funding, Inc., as servicer, Wells Fargo Bank, N.A., as trust
administrator, master servicer, servicer and back-up servicer and U.S. Bank
National Association, as trustee.

10.2 Assignment and Assumption Agreement, dated as of September 29, 2004 by and
between DLJ Mortgage Capital, Inc. and Credit Suisse First Boston Mortgage
Securities Corp.



                                         SIGNATURES

      Pursuant to the requirements of the Securities  Exchange Act of 1934, as amended,  the
registrant  has duly  caused  this  report  to be signed  on its  behalf by the  undersigned
hereunto duly authorized.



Dated:  September 29, 2004



                                    CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.


                                    By:  /s/ John P. Graham
                                         John P. Graham
                                         Vice President




                                       Exhibit Index


Exhibit Number          Description


 10.1                   Pooling  and  Servicing  Agreement  dated as of  September  1, 2004,
                        among Credit  Suisse  First Boston  Mortgage  Securities  Corp.,  as
                        depositor, DLJ Mortgage Capital, Inc., as seller,  Washington Mutual
                        Mortgage  Securities Corp, as seller and servicer,  Select Portfolio
                        Servicing, Inc., as servicer,  GreenPoint Mortgage Funding, Inc., as
                        servicer,  Wells Fargo Bank,  N.A., as trust  administrator,  master
                        servicer,  servicer  and back-up  servicer  and U.S.  Bank  National
                        Association, as trustee.

 10.2                   Assignment and Assumption Agreement, dated as of September 29,  2004
                        by and between DLJ Mortgage  Capital,  Inc. and Credit  Suisse First
                        Boston Mortgage Securities Corp.

CSFB ADJUSTABLE RATE MORTGAGE TRUST 2004-1 8-K