Between 1979 and 1984, 321 patients received 354 St. Jude Medical prostheses (194 aortic, 94 mitral, 1 tricuspid, and 32 multiple valve replacements). Follow-up was 96% complete (2967 patient-years; mean 9.5 years per patient). Actuarial event-free rates at 10 years and linearized rates (in parentheses) of late complications were as follows: embolism, 85.0% +/- 2.3% (2.3% per patient-year); anticoagulant-related hemorrhage, 74.8% +/- 2.7% (3.3% per patient-year); cerebrovascular accident, 81.8% +/- 2.5% (2.6% per patient-year); prosthesis thrombosis, 98.5% +/- 0.7% (0.1% per patient-year); endocarditis, 97.2% +/- 1.1% (0.4% per patient-year); prosthesis dysfunction, 97.1% +/- 1.0% (0.4% per patient-year); hemolytic anemia, 98.5% +/- 0.7% (0.1% per patient-year); reoperation, 97.4% +/- 1.0% (0.4% per patient-year); overall mortality, 63.3% +/- 2.7% (4.2% per patient-year); and valve-related death (including sudden death), 84.7% +/- 2.2% (1.4% per patient-year). Independent preoperative risk factors were as follows: (1) for embolism, cardiac failure as indication for operation and history of prior systemic embolism; (2) for cerebrovascular accidents, the same two factors and age; (3) for endocarditis, diabetes, chronic alcoholism, and aortic valve replacement; (4) for overall mortality, age, ejection fraction (or cardiac index or cardiothoracic index), chronic alcoholism, and history of systemic embolism; and (5) for valve-related death, chronic alcoholism, degenerative cause of valve disease, and prosthetic diameter 23 mm or smaller. Ninety percent of survivors were in New York Heart Association functional class I or II at the end of follow-up. In conclusion, this study confirms the excellent durability of the St. Jude Medical valve and the remarkable functional benefit for the majority of the patients. However, prosthesis-related complications are still common, particularly for small-diameter prostheses. Outcome is strongly related to the patient's preoperative cardiac condition and to the adequacy of anticoagulation control.