Exhibit 15

PricewaterhouseCoopers LLP

300 Madison Avenue

New York NY 10017

Telephone (646) 471-3000

www.pwc.com

May 7, 2010

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Commissioners:

We are aware that our report dated May 7, 2010 on our review of interim financial information of Arch Capital Group Ltd. and its subsidiaries (the “Company”) for the three month periods ended March 31, 2010 and March 31, 2009 and included in the Company’s quarterly report on Form 10-Q for the quarter ended March 31, 2010 is incorporated by reference in the Registration Statement on Forms S-3 (Registration No. 333-158309, Registration No. 33-34499, Registration No. 333-82612, Registration No. 333-110190 and Registration No. 333-117099) and in the Registration Statements on Forms S-8 (Registration No. 33-99974, Registration No. 333-86145, Registration No. 333-72182, Registration No. 333-82772, Registration No. 333-98971, Registration No. 333-124422 and Registration No. 333-142835).

Very truly yours,

/s/ PricewaterhouseCoopers LLP