Exhibit 15 [Letterhead of PricewaterhouseCoopers] Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Commissioners: We are aware of the incorporation by reference in the Registration Statement on Form S-3 (Registration No. 33-34499) and in the Registration Statements on Form S-8 (Registration No. 33-99974 and Registration No. 333-86145) of Arch Capital Group Ltd. of our review report dated May 14, 2001 (issued pursuant to the provisions of Statement of Auditing Standards No. 71) appearing in this Form 10-Q. Very truly yours, /s/ PricewaterhouseCoopers PricewaterhouseCoopers Hamilton, Bermuda May 15, 2001