For Shareholders

HAMILTON, Bermuda, July 31 /PRNewswire-FirstCall/ -- White Mountains Insurance Group, Ltd. (NYSE: WTM) announced today that it is reorganizing its reinsurance business by converting its Bermuda reinsurance operations into a branch of White Mountains Re Sirius. Warren Trace, currently President and CEO of White Mountains Re Bermuda, will remain in charge of the Bermuda branch operations, reporting to Goran Thorstensson, President and CEO of Sirius. The reorganization is expected to be effective on September 1, 2009 following receipt of required regulatory approvals.

Allan Waters, President and CEO of White Mountains Re, said, "This reorganization keeps our successful Bermuda reinsurance team in place while bringing the security of the whole Sirius balance sheet to our clients in Bermuda. Our team is excited about the new structure and looks forward to continuing our strong relationships with all our brokers and clients."

White Mountains Re will contribute in excess of $200 million of capital to Sirius, which will have in excess of $1.6 billion of regulatory capital on a pro forma basis as of June 30, 2009. In addition, approximately $400 million of capital will be upstreamed to the White Mountains Re and White Mountains holding companies.

White Mountains Reinsurance Company of America will remain under the direction of Dwight Evans as President and CEO. The White Mountains Re America underwriting platform and regulatory capitalization, which approximated $750 million as of June 30, 2009, will not be affected by the reorganization.

Additional Information

White Mountains is a Bermuda-domiciled financial services holding company traded on the New York Stock Exchange and the Bermuda Stock Exchange under the symbol WTM. Additional financial information and other items of interest are available at the Company's web site located at www.whitemountains.com.

 Safe Harbor Statement under the Private Securities Litigation Reform Act of
                                     1995

This press release may contain "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. All statements, other than statements of historical facts, included or referenced in this release which address activities, events or developments which we expect or anticipate will or may occur in the future are forward-looking statements. The words "will," "believe," "intend," "expect," "anticipate," "project," "estimate," "predict" and similar expressions are also intended to identify forward-looking statements. These forward-looking statements include, among others, statements with respect to White Mountains':

        X    changes in adjusted book value per share or return on equity;
        X    business strategy;
        X    financial and operating targets or plans;
        X    incurred losses and the adequacy of its loss and loss adjustment
             expense reserves and related reinsurance;
        X    projections of revenues, income (or loss), earnings (or loss) per
             share, dividends, market share or other financial forecasts;
        X    expansion and growth of our business and operations; and
        X    future capital expenditures.

These statements are based on certain assumptions and analyses made by White Mountains in light of its experience and perception of historical trends, current conditions and expected future developments, as well as other factors believed to be appropriate in the circumstances. However, whether actual results and developments will conform to our expectations and predictions is subject to a number of risks and uncertainties that could cause actual results to differ materially from expectations, including:

        X    the risks associated with Item 1A of White Mountains' 2008 Annual
             Report on Form 10-K;
        X    claims arising from catastrophic events, such as hurricanes,
             earthquakes, floods or terrorist attacks;
        X    the continued availability of capital and financing;
        X    general economic, market or business conditions;
        X    business opportunities (or lack thereof) that may be presented to
             it and pursued;
        X    competitive forces, including the conduct of other property and
             casualty insurers and reinsurers;
        X    changes in domestic or foreign laws or regulations, or their
             interpretation, applicable to White Mountains, its competitors or
             its clients;
        X    an economic downturn or other economic conditions adversely
             affecting its financial position;
        X    recorded loss reserves subsequently proving to have been
             inadequate;
        X    other factors, most of which are beyond White Mountains' control.

Consequently, all of the forward-looking statements made in this press release are qualified by these cautionary statements, and there can be no assurance that the actual results or developments anticipated by White Mountains will be realized or, even if substantially realized, that they will have the expected consequences to, or effects on, White Mountains or its business or operations. White Mountains assumes no obligation to publicly update any such forward-looking statements, whether as a result of new information, future events or otherwise.

                                                   CONTACT: Christine Repasy
                                                              (860) 368-2012

SOURCE  White Mountains Insurance Group, Ltd.

    -0-                           07/31/2009
    /CONTACT:  Christine Repasy of White Mountains Insurance Group, Ltd.,
+1-860-368-2012/
    /Web Site:  http://www.whitemountains.com /
    (WTM)

CO:  White Mountains Insurance Group, Ltd.; White Mountains Re Sirius; White
     Mountains Re Bermuda
ST:  Bermuda
IN:  INS FIN
SU:  RCN

PR
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9997 07/31/200908:00 EDThttp://www.prnewswire.com