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

August 24, 2004
Date of Report (date of earliest event reported)

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.

as Depositor and Master Servicer under a
Pooling and Servicing Agreement
dated as of August 1, 2004
providing for the issuance of

$301,582,806
(Approximate)

WaMu MORTGAGE PASS-THROUGH CERTIFICATES
SERIES 2004-CB3
(Exact name of Registrant as specified in its charter)

Delaware		333-103345		94-2528990
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

1201 THIRD AVENUE, WMT 1706
SEATTLE, WASHINGTON 98101
(Address of principal executive offices and Zip Code)

Registrant's telephone number, including area code: (206) 377-8555

(Former name or former 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):

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

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

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

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

SECTION 9 - FINANCIAL STATEMENTS AND EXHIBITS

ITEM 9.01 Financial Statements and Exhibits

The following exhibit is filed herewith:

4.1	Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp., as Depositor and Master Servicer, Citibank, N.A., as Trustee, and Christiana Bank & Trust Company, as Delaware Trustee, dated as of August 1, 2004.

The definition of Class C-Y Principal Reduction Amounts , included as Appendix 1 to the Pooling and Servicing Agreement, and the Mortgage Loan Schedule, included as Exhibit D to the Pooling and Servicing Agreement, have been intentionally omitted from this filing. Copies may be obtained from Washington Mutual Mortgage Securities Corp. or Citibank, N.A. by contacting:

in the case of Washington Mutual Mortgage Securities Corp.,

        Laura Kelsey
        Master Servicing Department
        Washington Mutual Mortgage Securities Corp.
        75 N. Fairway Drive,VHF2A01
        Vernon Hills, IL 60061
        Telephone: (847) 393-5198
        Facsimile:     (847) 549-2997

in the case of Citibank, N.A.,

        Karen Schluter
        Citibank, N.A.
        111 Wall Street
        14th Floor, Zone 3
         New York, NY 10005
        Telephone:  (212) 657-7781
        Facsimile:    (212) 657-4009

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.

		WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Date: September 8, 2004		By:		/s/ David H. Zielke David H. Zielke First Vice President and Counsel (Authorized Officer)

Exhibit Index

Exhibit No.	Description

4.1	Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp., as Depositor and Master Servicer, Citibank, N.A., as Trustee, and Christiana Bank & Bank Trust Company, as Delaware Trustee, dated as of August 1, 2004.

WaMu Mortgage Pass-Through Certificates, Series 2004-CB3 8-K