UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


                                    FORM 10-K

[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 or any amendment to this
Form 10-K. [X]

Documents incorporated by reference:  None



<PAGE>

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

PART I

Item 1.  Business

         Omitted.

Item 2.  Properties

         Omitted.

Item 3.  Legal Proceedings

The  Registrant is not aware of any material legal  proceeding  with respect to,
the Company, the Master Servicer, the Servicers,  the Trust Administrator or the
Trustee, in each case if applicable, as related to the Trust.

Item 4.  Submission of Matters to a Vote of Security Holders

No  matter  was  submitted  to a vote  or  consent  of  Holders  of the  Offered
Certificates during the fiscal year covered by this report.


PART II

Item 5.  Market for Registrant's Common Equity and Related Stockholder Matters

The Trust does not issue stock. There is currently no established secondary
market for the Certificates.  As of  December  31,  2002,  the number
of holders  of each  Class  of  Offered  Certificates was 38.


Item 6.  Selected Financial Data

         Omitted.

Item 7.  Management's Discussion and Analysis of Financial condition and
         Results of Operations

         Omitted.

Item 8.  Financial Statements and Supplementary Data

         Omitted.

Item 9.  Changes in and Disagreements with Accountants on Accounting and
         Financial Disclosure

There was no change of  accountants  or  disagreement  with  accountants  on any
matter of accounting principles or practices or financial disclosure.

                                      -2-

<PAGE>

PART III

Item 10. Directors and Executive Officers of the Registrant

         Omitted.

Item 11. Executive Compensation

         Omitted.

Item 12. Security Ownership of Certain Beneficial Owners and Management

         Omitted.


Item 13. Certain Relationships and Related Transactions

No reportable transactions have occurred.


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  Servicers'  Statement of  Compliance,  filed as Exhibit 99.1 hereto.
   Annual Statement of  Independent  Accountants  Report for the Servicers,
   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>
Annual report  pursuant to Section 13 or 15(d) of the  Securities  Exchange
Act of 1934 for the fiscal year ended December 31, 2002


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

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 31, 2003       By: /s/   Matt Ruppel
                                --------------------------------------
                          Name:  Matt Ruppel
                         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, Matt Ruppel, certify that:

     1. I have reviewed this annual report on Form 10-K, 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 31, 2003

By:     /s/  Matt Ruppel
        --------------------------------------

Name:   Matt Ruppel
Title:  Vice President


                                      -5-
<page>

SUPPLEMENTAL  INFORMATION TO BE FURNISHED WITH REPORTS FILED PURSUANT TO SECTION
15(D) OF THE ACT BY REGISTRANTS WHICH HAVE NOT REGISTERED SECURITIES PURSUANT TO
SECTION 12 OF THE ACT.

The  registrant  has not sent an annual report or proxy material to its security
holders.  The registrant  will not be sending an annual report or proxy material
to its security holders subsequent to the filing of this form.

                                      -6-
<PAGE>


                                 EXHIBIT INDEX

Exhibit     Description

 99.1       Servicers' Annual Statement of Compliance
 99.2       Servicers' Annual Independent Accountant's Report



                                      -7-




EXHIBIT 99.1 - Servicers' Annual Statement of Compliance
  To be supplied upon receipt by the Trustee

                                      -8-


EXHIBIT 99.2 - Servicers' Annual Independent Accountant's Report
  To be supplied upon receipt by the Trustee

                                      -9-