Aspen Insurance Holdings Limited : Aspen Provides Initial Estimate for Floods in Thailand and Updates Previous 2011 Catastrophe Loss Estimates

Aspen Insurance Holdings Limited ("Aspen") (NYSE: AHL) today announces an initial estimate of losses of $54 million, net of applicable reinsurance, reinstatement premiums and tax, for the flooding in Thailand. This is consistent with estimated industry insured losses of $15 billion arising from widespread flooding, which occurred in Thailand in October and November 2011.

Aspen's estimate is based on its review of the market insured loss, the individual treaties and policies expected to be impacted, and discussions with clients and brokers. Given the complexity of this event, there is considerable uncertainty associated with this estimate and actual losses may differ materially.

Aspen also announces an increase in its aggregate estimate of losses for natural catastrophes occurring in the first nine months of 2011 of $48 million, net of applicable reinsurance, reinstatement premiums and tax. This is primarily due to a $36 million increase in Aspen's loss estimate for the Tohoku earthquake as a result of new information in respect of a major Japanese mutual, to which Aspen is now assuming a total loss from its participation.

About Aspen Insurance Holdings Limited ("the Company")

The Company provides reinsurance and insurance coverage to clients in various domestic and global markets through wholly-owned subsidiaries and offices in Bermuda, France, Germany, Ireland, Singapore, Switzerland, the United Kingdom and the United States. For the twelve months ended December 31, 2010, the Company reported gross written premiums of $2,076.8 million, net income of $312.7 million and total assets of $8.8 billion. Its operating subsidiaries have been assigned a financial strength rating of "A" ("Strong") by Standard & Poor's, an "A2" ("Excellent") by A.M. Best and an "A2" ("Good") by Moody's Investors Service.

Application of the Safe Harbor of the Private Securities Litigation Reform Act of 1995

This press release contains written, and Aspen's officers may make related oral, "forward-looking statements" within the meaning of the US federal securities laws regarding its initial estimate of losses from the severe weather events that occurred in 2011 through the fourth quarter. These statements are made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements include all statements that do not relate solely to historical or current facts, and can be identified by the use of words such as "expect," "intend," "plan," "believe," "project," "anticipate," "seek," "will," "estimate," "may," "continue," and similar expressions of a future or forward-looking nature.

All forward-looking statements address matters that involve risks and uncertainties. Accordingly, there are or will be important factors that could cause actual results to differ materially from those indicated in these statements. Aspen believes these factors include, but are not limited to, developing information available from brokers, clients and loss adjusters, the receipt of actual loss reports, forecasts of losses relating to these events for the industry as a whole and for individual companies, changes in the total industry losses or the Company's share of such losses, the actual number of the Company's insureds incurring losses from these events, limitations in current modeling techniques and their application, the impact of any demand surge on claims, coverage issues, the impact of foreign exchange fluctuations and the effectiveness of any of the Company's loss limitation methods. For a more detailed description of these uncertainties and other factors which could cause results to differ materially, please see the "Risk Factors" section in Aspen's Annual Report on Form 10-K as filed with the US Securities and Exchange Commission on February 25, 2011.

Aspen undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the dates on which they are made.

Aspen
Investors:
Kerry Calaiaro, [phone]
Senior Vice President, Investor Relations
[e-mail]
or
Media:
Tim Dickenson, [phone]
Global Head of Communications
[e-mail]
or
North America ? Abernathy MacGregor
Allyson Morris, [phone]
[e-mail]
or
Europe and Asia ? Citigate Dewe Rogerson
Justin Griffiths, [phone]
[e-mail]