UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


                                   FORM 10-K/A

[X]      Annual  report  pursuant  to  Section  13 or  15(d)  of the Securities
         Exchange   Act  of  1934   for   the    period  from  April 1, 2002
         (Commencement of Operations) to December 31, 2002

[  ]     Transition report pursuant to Section 13 or 15(d) of the
         Securities Exchange Act of 1934 for the transition period from   to


                        Commission File Number 333-77054-12

               CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.
             (Exact name of registrant as specified in its charter)

         Delaware                                            13-3320910
(State or other jurisdiction of                           I.R.S. Employer
incorporation or organization)                            Identification No.)

11 Madison Ave.
New York, New York                                             10010
(Address of Principal Executive Offices)                      (Zip Code)

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


              CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.
         CSFB Mortgage-Backed Pass-Through Certificates, Series 2002-S12
            (Title of each class of securities covered by this Form)

        Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act:  None

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the  preceding 12 months (or for such  shorter  period that the  registrant  was
required  to file  such  reports),  and  (2) has  been  subject  to such  filing
requirements for the past 90 days. Yes [X] No [ ]

Indicate by check mark if disclosure of delinquent  filers  pursuant to Item 405
of Regulation  S-K is not contained  herein,  and will not be contained,  to the
best of registrant's  knowledge,  in definitive proxy or information  statements
incorporated  by  reference  in Part III of this Form 10-K/A or any amendment to
this Form 10-K/A. [X]

Documents incorporated by reference:  None

<PAGE>

                             AMENDMENT NUMBER 1 OF 1

                                       -2-

<PAGE>

CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.
CSFB Mortgage-Backed Pass-Through Certificates, Series 2002-S12
-----------------------------------------------------------------------


PART IV

Item 14. Exhibits, Financial Statement Schedules and Reports on Form 8-K

(a) The following documents are filed as part of this report:

    (1) Financial Statements:
         Omitted.

    (2)  Financial Statement Schedules:
         Omitted.

    (3)  Exhibits:

     Annual  Independent  Accountant's  Servicing Reports  concerning  servicing
activities for the year ended December 31, 2002, filed as Exhibit 99.1 hereto.

     Report of Management as to Compliance with Minimum Servicing  Standards for
the year ended December 31, 2002, filed as Exhibit 99.2 hereto.

(b)   Reports on Form 8-K: The  following  Current  Reports on Form 8-K were
      filed by the Registrant during the last quarter of 2002.

     Current Reports on Form 8-K, dated October 25, 2002, November 25, 2002, and
December  26, 2002,  were filed for the purpose of filing the Monthly  Statement
sent to the Holders of the Offered  Certificates  for payments  made on the same
dates. The items reported in such Current Report were Item 5 (Other Events).


(c)   Exhibits to this report are listed in Item (14)(a)(3) above.

                                      -3-
<PAGE>

CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.
CSFB MORTGAGE PASS-THROUGH CERTIFICATES, SERIES 2002-S12
--------------------------------------------------------


Annual report  pursuant to Section 13 or 15(d) of the  Securities  Exchange
Act of 1934 for the fiscal year ended December 31, 2002


SIGNATURE

Pursuant to the  requirements of Section 13 or 15(d) of the Securities  Exchange
Act of 1934,  the  registrant  has duly  caused  this report to be signed on its
behalf by the undersigned thereunto duly authorized.


                           CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP.

Date: March 25, 2004       By: /s/   Andrew Kimura
                               --------------------------------------
                           Name:  Andrew Kimura
                           Title:  Vice President



                                      -4-
<PAGE>

                                 CERTIFICATION

         Re:      Credit Suisse First Boston Mortgage Securities Corp.,
                  CSFB Trust Series 2002-S12
                  CSFB Mortgage Pass-Through Certificates, Series 2002-S12

                  I, Andrew Kimura, certify that:

     1. I have reviewed  this annual  report on Form 10-K/A,  and all reports on
Form 8-K  containing  distribution  and  servicing  reports  filed in respect of
periods included in the year covered by this annual report, of CSFB Trust Series
2002-S12 (the "Trust");

     2. Based on my knowledge,  the  information  in these  reports,  taken as a
whole, does not contain any untrue statement of a material fact or omit to state
a  material  fact  necessary  to make  the  statements  made,  in  light  of the
circumstances  under which such  statements  were made, not misleading as of the
last day of the period covered by this annual report;

     3. Based on my  knowledge,  the  distribution  information  required  to be
prepared  by the Trustee  based upon the  servicing  information  required to be
provided by each Servicer under the Pooling and Servicing  Agreement is included
in these reports;

     4. Based on my knowledge and upon the annual compliance statements included
in the report and required to be delivered to the Trustee in accordance with the
terms of the Pooling and Servicing  Agreement and based upon the review required
under the  Pooling  and  Servicing  Agreement,  and except as  disclosed  in the
report,  each  Servicer  has  fulfilled  its  obligations  under the Pooling and
Servicing Agreement; and

     5. The  reports  disclose  all  significant  deficiencies  relating to each
Servicer's  compliance with the minimum servicing standards based, in each case,
upon the report provided by an independent public accountant, after conducting a
review in compliance  with the Uniform Single  Attestation  Program for Mortgage
Bankers or similar standard as set forth in the Pooling and Servicing Agreement,
that is included in these reports.

     Capitalized terms used but not defined herein have the meanings ascribed to
them in the Pooling and Servicing  Agreement,  dated April 1, 2002 (the "Pooling
and Servicing Agreement"),  among Credit Suisse First Boston Mortgage Securities
Corp., as depositor (the  "Depositor"),  DLJ Mortgage  Capital,  Inc., as seller
(the "Seller"),  Wilshire Credit Corporation, as a servicer (in such capacity, a
"Servicer"),  Ocwen  Federal  Bank  FSB,  as a  servicer  (in such  capacity,  a
"Servicer") and JPMorgan Chase Bank, as trustee (the "Trustee").

Dated:  March 25, 2004

By:     /s/  Andrew Kimura
        --------------------------------------

Name:   Andrew Kimura
Title:  Vice President


                                      -5-
<page>




                                 EXHIBIT INDEX

Exhibit Description

99.1    Annual Independent Accountant's Servicing Report for the year ended
        December 31, 2002

        a) Wilshire Credit Corporation
        b) Ocwen Federal Bank FSB

99.2    Report of Management as to compliance with minimum servicing standards
        for the year ended December 31, 2002.

        a) Wilshire Credit Corporation
        b) Ocwen Federal Bank FSB

                                      -6-
<page>




                                  EXHIBIT 99.1
      Annual Independent Accountant's Servicing Report for the year ended
                                December 31, 2002


                                      -7-




Deloitte & Touche, LLP
111 SW Fifth Avenue
Portland, Oregan 97204
www.deloitte.com



INDEPENDENT ACCOUNTANTS' REPORT


TO:  Wilshire Credit Corporation:

     We have examined management's assertion about Wilshire Credit Corporation's
(the "Company"),  a wholly-owned subsidiary of Wilshire Financial Services Group
Inc., compliance with the minimum servicing standards identified in the Mortgage
Bankers Association of America's Uniform Single Attestation Program for Mortgage
Bankers (USAP) as of and for the year ended  December 31, 2002,  included in the
accompanying  management assertion.  Management is responsible for the Company's
compliance with those minimum  servicing  standards.  Our  responsibility  is to
express an opinion on  management's  assertion  about the  Company's  compliance
based on our examination.

     Our examination  was made in accordance  with standards  established by the
American  Institute of Certified Public Accountants and,  accordingly,  included
examining,  on a test basis,  evidence about the Company's  compliance  with the
minimum  servicing   standards  and  performing  such  other  procedures  as  we
considered  necessary  in the  circumstances.  We believe  that our  examination
provides a reasonable basis for our opinion.  Our examination does not provide a
legal  determination  on the  Company's  compliance  with the minimum  servicing
standards.

     In our opinion,  management's  assertion that the Company complied with the
aforementioned minimum servicing standards as of and for the year ended December
31, 2002 is fairly stated in all material respects.

By:  /s/ Deloitte & Touche, LLP
--------------------------------

March 13, 2003


                                       -8-



<page>

PricewaterhouseCoopers, LLP
222 Lakeview Avenue
Suite 360
West Palm Beach, FL  33401
Telephone:  (561) 832-0038
Facsimile:  (561) 803-0181


REPORT OF INDEPENDENT ACCOUNTANTS


To the Board of Directors of
Ocwen Federal Bank FSB


     We have  examined  management's  assertion,  included  in the  accompanying
Management  Assertion on Compliance with USAP, that, except fo the noncompliance
related to interest on escrows  described in the third paragraph,  Ocwen Federal
Bank FSB (the "Bank") complied with the minimum servicing  standards  identified
in the Mortgage  Bankers  Association  of  America's  ("MBA's")  Uniform  Single
Attestation  Program for Mortgage  Bankers ("USAP") as of and for the year ended
December 31, 2002.  Management is  responsible  for the Bank's  compliance  with
those minimum servicing  standards.  Our responsibility is to express an opinion
on management's assertion about the Bank's compliance based on our examination.

     Our examination  was made in accordance  with standards  established by the
American  Institute of Certified Public Accountants and,  accordingly,  included
examining,  on a test  basis,  evidence  about the  Bank's  compliance  with the
minimum  servicing   standards  and  performing  other  such  procedures  as  we
considered  necessary  in the  circumstances.  We believe  that our  examination
provides a reasonable basis for our opinion.  Our examination does not provide a
legal  determination  on  the  Bank's  compliance  with  the  minimum  servicing
standards.

     Our examination disclosed noncompliance with minimum servicing standards in
certain states related to interest on escrows  applicable to the Bank during the
year  ended  December  31,  2002.  Such   noncompliance   is  described  in  the
accompanying Management Assertion on Compliance with USAP.

     In our opinion,  management's  assertion  that the Bank  complied  with the
aforementioned   minimum  servicing  standards,   except  for  noncompliance  as
described in the accompanying  Management  Assertion on Compliance with USAP, as
of and for the year ended  December 31, 2002 is fairly  stated,  in all material
respects.


By:  /s/PricewaterhouseCoopers, LLC
------------------------------------
PricewaterhouseCoopers, LLC


March 14, 2003

                                      -9-

<page>


                                  EXHIBIT 99.2
     Report of Management as to compliance with minimum servicing standards
                      for the year ended December 31, 2002


                                      -10-


<page>

Wilshire Credit Corporation
P. O. Box 8517
Portland, Oregon
97207-8517



                              MANAGEMENT ASSERTION

     As of and for the year ended December 31, 2002, Wilshire Credit Corporation
has complied in all material respects with the minimum  servicing  standards set
forth  in  the  Mortgage  Bankers   Association  of  America's   Uniform  Single
Attestation  Program  for  Mortgage  Bankers.  As of and for this  same  period,
Wilshire  Credit  Corporation  had in effect a  fidelity  bond in the  amount of
$10,000,000.00   and  an  errors   and   omissions   policy  in  the  amount  of
$5,000,000.00.



By:  /s/ Heidi Peterson                  Company:  Wilshire Credit Corporation
     --------------------------
     Heidi Peterson

     Vice President                     Date:  August 4, 2003
     Investor Relations

                                      -11-


<page>

OCWEN FEDERAL BANK FSB
1675 Palm Beach Lakes Boulevard
West Palm Beach, FL  33401

                  MANAGEMENT ASSERTION ON COMPLIANCE WITH USAP

March 14, 2003

     As of and for the year ended  December  31,  2002,  except as  specifically
noted  below,  Ocwen  Federal Bank FSB (the "Bank") has complied in all material
respects with the minimum servicing  standards set forth in the Mortgage Bankers
Association  of  America's  ("MBA's")  Uniform  Single  Attestation  Program for
Mortgage Bankers ("USAP").

..  Standard: Interest on escrow accounts shall be paid, or credited, to
   mortgagors in accordance with the applicable state laws.

Interest on escrow  accounts in certain  states was not paid,  or  credited,  to
mortgagors in accordance  with the  applicable  state laws during the year ended
December 31, 2002.  The Bank is currently  implementing  an  enhancement  to its
REALServicing  servicing  system to  ensure  that for  loans  collateralized  by
properties  located in states  that  require  the  payment of interest on escrow
accounts,  the  payment or  crediting  of such  interest is in  accordance  with
applicable state laws.

     As of and for this same period,  the Bank has in effect a fidelity  bond in
the amount of  $15,000,000  and an errors and omissions  policy in the amount of
$10,000,000.



/s/ Ronald M. Faris
---------------------------
Ronald M. Faris
President

/s/ Scott W. Anderson
---------------------------
Scott W. Anderson
Senior Vice President of Residential Assets

/d/ James D. Campbell
---------------------------
James D. Campbell
Director of Investor Reporting




OCWEN FEDERAL BANK FSB
1675 Palm Beach Lakes Boulevard
West Palm Beach, FL  33401

OFFICER'S CERTIFICATION ON ANNUAL STATEMENT AS TO COMPLIANCE

March 13, 2002

     Pursuant to the applicable sections of the Servicing Agreements,  I, Ronald
M. Faris,  as officer of Ocwen  Federal Bank,  FSB (the "Bank"),  confirm that a
review of he  activities  of the Bank during the calendar  year ending  December
31,200 and of the performance under the Servicing  Agreements has been made uner
my supervision.  To the best of my knowledge, based on such review, the Bank has
fulfilled all of its obligations under the Servicing Agreements  throughout such
calendar year.

/s/ Ronald M. Faris
---------------------------
Ronald M. Faris
President, Ocwen Federal Bank FSB

                                      -12-