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:  September 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.
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   Address:      80 South Main Street
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                 Hanover, New Hampshire 03755
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                 U.S.A.
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Form 13F File Number: 28-01681
                         ---------------------

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:   Chief Accounting Officer
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Phone:   (603) 640-2200
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Signature, Place, and Date of Signing:

    /s/ J. Brian Palmer               Hanover, New Hampshire   November 15, 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).)




                             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
                                        --------------------
                                            (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.

None