Wamu Mortgage Pass Through Certificates 2002-S1 Sample Contracts

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 23rd, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200301 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 23rd, 2004)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 04/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.43073% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 23rd, 2004)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 02/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.43601% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 23rd, 2004)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 03/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.43024% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 4th, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200405 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (May 4th, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200404 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (April 5th, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200403 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (March 3rd, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200402 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (February 4th, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200401 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (January 7th, 2004)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200312 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (December 4th, 2003)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200311 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (November 4th, 2003)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200310 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (October 9th, 2003)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200309 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (September 4th, 2003)

The Class Principal Balances of each Class of the Class CB1,CB2,CB3,CB4,CB5,CB6 Certificatesimmediately after the principal and interest distribution on 200308 are as follows:

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (August 11th, 2003)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 07/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.42708% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (July 7th, 2003)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 06/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.42603% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (June 10th, 2003)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 05/2003 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.43049% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (January 3rd, 2003)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 12/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.44606% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (December 9th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 11/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.45027% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (November 8th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 10/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.45389% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (October 7th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 09/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.45653% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (September 10th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 08/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.45837% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (August 8th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 07/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.46006% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (July 9th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 06/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.46059% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WAMU MORTGAGE PASS-THROUGH CERTIFICATES, (June 7th, 2002)

SECURITIES AND EXCHANGE COMMISSION 450 Fifth Street, NW Washington, DC 20549 ------------------------------------------ FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the Month of May, 2002 WAMU MORTGAGE PASS-THROUGH CERTIFICATES, SERIES: 2002-s1 (Exact name of the registrant as specified in charter) Delaware 333-77026-01 94-2528990 (State or other (Commission (IRS Employer jurisdiction of File Number) Identification Incorporation)

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (May 9th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 04/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.46133% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (April 10th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 03/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.46153% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. (March 11th, 2002)

EXHIBIT 99 WASHINGTON MUTUAL MORTGAGE SECURITIES CORP. MASTER SERVICING MORTGAGE PASS-THROUGH CERTIFICATES 02/2002 DISTRIBUTION REPORT SERIES: wamu 2002-s1 WEIGHTED AVERAGE PC RATE: 6.46171% POOL NUMBER: Group 1 = 1814 ____________________________________________________________________________________________ ISSUE DATE: 01/25/2002 CERTIFICATE BALANCE AT ISSUE: $477,328,678.67 CERTIFICATE TOTAL ACCOUNT CERTIFICATE NUMBER OF ACTIVITY BALANCE MORTGAGES (@PC RATE) OUTSTANDING

Wamu Mortgage Pass Through Certificates 2002-S1 – POOLING AND SERVICING AGREEMENT (February 8th, 2002)

EXECUTION VERSION WASHINGTON MUTUAL MORTGAGE SECURITIES CORP., as Depositor and Master Servicer and STATE STREET BANK AND TRUST COMPANY, as Trustee and CHRISTIANA BANK & TRUST COMPANY, as Delaware Trustee POOLING AND SERVICING AGREEMENT $634,874,064.00 Washington Mutual Mortgage Securities Corp. WaMu Mortgage Pass-Through Certificates Series 2002-S1 Cut-Off Date: January 1, 2002 TABLE OF CONTENTS