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)

27-Dec-04

Credit Suisse First Boston Mortgage Securities Corp., Home Equity Pass-Through Certificates Series 2004-AA1

Credit Suisse First Boston Mortgage Securities Corp.

(Exact Name of Registrant as Specified in its Charter)

Delaware

333-107055-40

13-3320910

(State or Other Jurisdiction

Of Incorporation)

(Commission

File Number)

(I.R.S. Employer

Identification No.)

11 Madison Avenue

New York, New York

(Address of Principal
Executive Offices)

10010

(Zip Code)

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

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 communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

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

[ ] 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))

Item 8.01 Other Events.

On 27-Dec-04 a scheduled distribution was made from the Trust to holders of the Certificates. The Trustee has caused to be filed with the Commission, the Monthly Report dated 27-Dec-04. The Monthly Report is filed pursuant to and in accordance with (1) numerous no-action letters (2) current Commission policy in the area.

Item 9.01 Financial Statements and Exhibits.

Exhibit No. 99.1

Monthly Distribution Report dated: 27-Dec-04

SIGNATURES

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

By: U.S. Bank National Association, as Trustee for:

Credit Suisse First Boston Mortgage Securities Corp.,

Home Equity Pass-Through Certificates

Series 2004-AA1

By:

/s/ Sheryl Christopherson

Name:

Sheryl Christopherson

Title:

Vice President

Dated: 03-Jan-05

Index to Exhibits

Exhibit No. 99.1

Monthly Distribution Report dated: 27-Dec-04

CSFB Home Equity Pass-Through 2004-AA1 8-K