EXHIBIT 21 PMA CAPITAL CORPORATION SIGNIFICANT SUBSIDIARIES OF REGISTRANT AS OF DECEMBER 31, 1998 PMA Capital Corporation (Pennsylvania) PMA Reinsurance Corporation (Pennsylvania) Caliber One Indemnity Company (Delaware) Pennsylvania Manufacturers' Association Insurance Company (Pennsylvania) PMA Management Corporation (Pennsylvania) PMA Services Incorporated (Pennsylvania) Presque Enterprises Incorporated (Pennsylvania) Pennsylvania Manufacturers Indemnity Company (Pennsylvania) Manufacturers Alliance Insurance Company (Pennsylvania) Mid Atlantic States Investment Company (Delaware) Mid-Atlantic States Casualty Company (Pennsylvania) PMA Holdings Cayman, Ltd. PMA International Insurance Cayman, Ltd. High Mountain Reinsurance, Ltd. (Cayman) Caliber One Management Company, Inc. (Delaware) PMA Holdings Limited (Bermuda) Pennsylvania Manufacturers International Insurance, Ltd. (Bermuda) PMA Life Insurance Company (Pennsylvania)