UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   FORM 13F

                              FORM 13F COVER PAGE


Report for the Calendar Year or Quarter Ended: December 31, 2009.
                                               -----------------------

Check Here if Amendment / /; Amendment Number:
                                               ---------
   This Amendment (Check only one.):    / / is a restatement.
                                        / / adds new holdings entries.

Institutional Investment Manager Filing this Report:

   Name:         White Mountains Insurance Group, Ltd.
                 -------------------------------------
   Address:      80 South Main Street
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                 Hanover, New Hampshire 03755-2053
                 -------------------------------------
                 U.S.A.
                 -------------------------------------

Form 13F File Number: 028-01681
                          ---------------------

The institutional investment manager filing this report and the person by
whom it is signed hereby represent that the person signing the report is
authorized to submit it, that all information contained herein is true,
correct and complete, and that it is understood that all required items,
statements, schedules, lists, and tables, are considered integral parts of
this form.

Person Signing this Report on Behalf of Reporting Manager:

Name:    J. Brian Palmer
         -------------------------------------------
Title:   Vice President and Chief Accounting Officer
         -------------------------------------------
Phone:   (603) 640-2200
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Signature, Place, and Date of Signing:

    /s/ J. Brian Palmer            Boston, Massachusetts   February 16, 2010
-------------------------------    ---------------------   -----------------
        [Signature]                  [City, State]               [Date]

Report Type (Check only one.):

/ / 13F HOLDINGS REPORT. (Check here if all holdings of this reporting
    manager are reported in this report.)

/ / 13F NOTICE. (Check here if no holdings reported are in this report,
    and all holdings are reported by other reporting manager(s).)

/X/ 13F COMBINATION REPORT. (Check here if a portion of the holdings for this
    reporting manager are reported in this report and a portion are reported by
    other reporting manager(s).)

List of Other Managers Reporting for this Manager:
[If there are no entries in this list, omit this section.]

    Form 13F File Number         Name

    028-12951                    OneBeacon Insurance Group, Ltd.
        ---------------          ------------------------------------
    028-00470                    White Mountains Advisors LLC
        ---------------          ------------------------------------




                             FORM 13F SUMMARY PAGE

Report Summary:


Number of Other Included Managers:                0
                                        --------------------

Form 13F Information Table Entry Total:           1
                                        --------------------

Form 13F Information Table Value Total:        $363
                                        --------------------
                                            (thousands)


List of Other Included Managers:

Provide a numbered list of the name(s) and Form 13F file number(s) of all
institutional investment managers with respect to which this report is filed,
other than the manager filing this report.

[If there are no entries in this list, state "NONE" and omit the column headings
and list entries.]

NONE



                      FORM 13F INFORMATION TABLE




      COLUMN 1               COLUMN 2       COLUMN 3 COLUMN 4         COLUMN 5         COLUMN 6    COLUMN 7          COLUMN 8
------------------------- ---------------- --------- -------- ---------------------- ------------ ---------- ----------------------
                                                      VALUE    SHRS OR   SH/   PUT/   INVESTMENT    OTHER       VOTING AUTHORITY
   NAME OF ISSUER          TITLE OF CLASS    CUSIP   (x$1000)  PRN AMT   PRN   CALL   DISCRETION   MANAGERS   SOLE   SHARED   NONE
------------------------- ---------------- --------- -------- --------- ----- ------ ------------ ---------- ------ -------- ------
                                                                                            
SIEMENS AG                SPONSORED ADR    826197501  $ 363     3,900     SH            SOLE          N/A     3,900