Paraprosthetic leak (PPL) is a rare but potentially serious complication of cardiac valve replacement. Between 1974 and 1988, 1175 prosthetic valves were implanted in 1026 patients by one cardiac surgeon at St. Thomas' Hospital, London. Of these 539 (52.5%) were aortic (AVR), 334 (32.6%) mitral (MVR), 7 (0.7%) tricuspid, and 144 (14%) AV and MV double valve replacements (DVR). There were only 2 triple valve replacements. The prosthetic valves implanted were the Starr-Edwards (7%), Bjork Shiley (11.8%), Lillehei-Kaster (23%), Carpentier-Edwards bioprosthesis (35.2%), Duromedics bileaflet (16.4%) and a variety of other mechanical and bioprosthetic valves (6.6%). Over the 15 year period there were a total of 82 (7%) valve failures of which PPL was diagnosed in 29 (2.5%) valves in 24 patients. Presenting features included cardiac decompensation in 72%, bacterial endocarditis in 12% and haemolytic anaemia in 12%. One patient (4%) had no symptoms. Nineteen patients underwent re-operation. Median time to re-operation was 15 months (range 1-65 months) with a re-operative mortality of 22%. Clinical evidence of prosthetic valve infection was found in 79% of MVR and 67% of AVR. A heavily calcified aortic annulus, found in 47% of patients, may also have contributed to PPL after AVR.