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

                                    FORM 13F
                               FORM 13F COVER PAGE

       INFORMATION REQUIRED OF INSTITUTIONAL INVESTMENT MANAGERS PURSUANT
  TO SECTION 13(f) OF THE SECURITIES EXCHANGE ACT OF 1934 AND RULES THEREUNDER

          Report for the Calendar Year or Quarter Ended  June 30  , 2004.
                                                        ---------

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 of Principal Executive Office:     80 South Main Street
                                           Hanover, New Hampshire 03755
                                           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 therein 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:   Chief Accounting Officer
Phone:   (603) 640-2200

Signature, Place, and Date of Signing:

/s/   J. Brian Palmer             Hanover, New Hampshire         August 16, 2004
--------------------------------------------------------------------------------
      [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.)

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

[ ]      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:

Form 13F File Number       Name
028-00470                  White Mountains Advisors, LLC





                              FORM 13F SUMMARY PAGE

Report Summary:

Number of Other Included Managers:                NONE
                                             --------------

Form 13F Information Table Entry Total:           NONE
                                             --------------

Form 13F Information Table Value Total:           NONE
                                             --------------

List of Other Included Managers:

Provide a numbered list of the names 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.

No.             Form 13F File Number               Name