For Shareholders

HAMILTON, Bermuda, Sept. 10, 2011 /PRNewswire via COMTEX/ --

White Mountains Insurance Group, Ltd. (NYSE: WTM) announced today the reorganization and rebranding of its global reinsurance business. All reinsurance operating entities will be consolidated under Sirius International Insurance Corporation (Sirius International) and the reinsurance group will operate as the Sirius Group (formerly White Mountains Re Ltd.). Sirius International's regulatory capital will increase to $2.2 billion pro forma for the reorganization.

Sirius America Insurance Company (Sirius America, formerly White Mountains Reinsurance Company of America) will be owned by Sirius International. It will retain approximately $600 million of statutory surplus and will receive $300 million of additional capital and stop loss support from its parent Sirius International.

Allan Waters, President and CEO of Sirius Group, said "This reorganization builds upon the highly successful Sirius track record and consolidates our operations into an efficient global platform. Clients of both Sirius International and Sirius America will benefit from Sirius International's $2.2 billion of pro forma regulatory capital. Sirius International will continue under the direction of Goran Thorstensson and his team and Dwight Evans will continue to lead the Sirius America team."

Group financial strength ratings from the four major ratings agencies are expected concurrently with the reorganization. The reorganization, subject to receipt of regulatory approvals, is expected to be completed in the fourth quarter.

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':

• changes in adjusted 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 and related reinsurance;
• projections of revenues, income (or loss), earnings (or loss) per share, dividends, market share or other financial forecasts;
• expansion and growth of our 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 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:

• the risks associated with Item 1A of White Mountains' 2010 Annual Report on Form 10-K;
• 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 property and casualty insurers and reinsurers;
• changes in domestic or foreign laws or regulations, or their interpretation, applicable to White Mountains, its competitors or its clients;
• an economic downturn or other economic conditions adversely affecting its financial position;
• recorded loss reserves subsequently proving to have been inadequate;
• actions taken by ratings agencies from time to time, such as financial strength or credit ratings downgrades or placing ratings on negative watch;
• 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.

SOURCE White Mountains Insurance Group, Ltd.