For Shareholders

HAMILTON, Bermuda, Apr 19, 2004 /PRNewswire-FirstCall via COMTEX/ -- White Mountains Insurance Group, Ltd. (NYSE: WTM) announced today the formation of White Mountains Re Group, Ltd., a Bermuda-based holding company, and the appointment of Steven Fass as its President and CEO. White Mountains Re will combine Folksamerica Re, Fund American Re and White Mountains Underwriting with the newly acquired Sirius Insurance Group to form a cohesive, global reinsurance organization. White Mountains' reinsurance operations now have combined regulatory capital of approximately $2 billion and over $2 billion in gross premiums. White Mountains Re will rank among the top 15 reinsurance organizations in the world.

White Mountains' CEO Ray Barrette said, "With the Sirius acquisition, Steve has built a significant global business for White Mountains. As CEO of White Mountains Re Group, Steve will make sure the operating companies continue the approach he developed at Folksamerica of conservative underwriting, careful capital management and opportunistic acquisitions. He and some of his key partners will now be based in Bermuda to oversee all of our reinsurance operations."

Edward Stanco has been appointed President and CEO of Folksamerica Re, replacing Steve Fass who has been appointed Chairman. Folksamerica Re will continue as the U.S. reinsurance arm of White Mountains Re.

Michael Maloney and Michael Tyburski join Steve Fass as the White Mountains Re holding company team serving as Managing Directors. Both were Executive Vice Presidents at Folksamerica Re.

Ron Stanziale, Senior Vice President and Chief Accounting Officer of Folksamerica Re, has been appointed Chief Financial Officer of Folksamerica Re.

Steve Fass said, "Ed is an outstanding professional with over 30 years of experience in the reinsurance field. At Folksamerica for the last two years, Ed, as Senior Vice President and Chief Domestic Treaty Officer of Folksamerica Re, has demonstrated both his technical skills and his leadership abilities. I am very comfortable about Folksamerica's future with Ed at the helm."

Steve continued, "Mike Tyburski and Mike Maloney are valued partners who have contributed significantly to the success of Folksamerica. Their knowledge and dedication will be invaluable to White Mountains Re."

Through Folksamerica Reinsurance Company, Sirius International Insurance Corporation and White Mountains Underwriting Limited, White Mountains Re offers lead capacity for most property, casualty, accident & health and marine exposures. Program business is written through Sirius America Insurance Company. Underwriting offices are located in New York, Stockholm, Chicago, Belgium, Miami, London, Connecticut, Bermuda, Hamburg, Toronto, Singapore and Dublin.

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 "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':

    -- growth in book value per share or return on equity;
    -- business strategy;
    -- financial and operating targets or plans;
    -- incurred losses and the adequacy of its loss and loss adjustment
        expense reserves;
    -- projections of revenues, income (or loss), earnings (or loss) per
        share, dividends, market share or other financial forecasts;
    -- expansion and growth of its business and operations; and
    -- 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 with its expectations and predictions is subject to a number of risks and uncertainties that could cause actual results to differ materially from expectations, including:

    -- the failure of the Sirius acquisition to enhance shareholder value;
    -- claims arising from catastrophic events, such as hurricanes,
       earthquakes, floods or terrorist attacks;
    -- the continued availability of capital and financing;
    -- general economic, market or business conditions;
    -- business opportunities (or lack thereof) that may be presented to it
       and pursued;
    -- competitive forces, including the conduct of other insurers and
       reinsurers;
    -- changes in domestic or foreign laws or regulations applicable to White
       Mountains, its competitors or its  clients;
    -- an economic downturn or other economic conditions adversely affecting
       its financial position;
    -- loss reserves established subsequently proving to have been inadequate;
       and
    -- 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 update publicly any such forward-looking statements, whether as a result of new information, future events or otherwise.

CONTACT:
David Foy
Tel: (203) 453-1681

SOURCE White Mountains Insurance Group, Ltd.

David Foy of White Mountains, 203-453-1681 (WTM)