To determine the long-term results of aortic valve replacement with the Smeloff-Cutter prosthesis, the fate of 358 of 459 (78%) consecutive patients was determined 1 to 12 years postoperatively. There were 319 male patients (70%). Mean age at operation was 57 years (range, 15 to 84 years). Aortic stenosis was the dominant lesion in 267 patients (58%) and aortic regurgitation in 133 patients (29%). Fifty-nine patients (13%) had both aortic stenosis and regurgitation. In addition to aortic valve replacement, 93 patients (20%) had coronary artery bypass, 30 (6.5%) had mitral commissurotomy, 23 (5%) had mitral valve replacement, and 41 (9%) had other procedures. Preoperative status by New York Heart Association Functional Class was: Class I, 3 (1%); Class II, 39 (8%); Class III, 148 (32%); and Class IV, 269 (59%). Operative (30-day) mortality was 8.5% (39 out of 459). Functional improvement was obtained in all postoperative survivors: 345 (82%), Class I; 63 (15%), Class II; and 12 (3%), Class III. A perivalvular leak developed in 6 patients (1%) and subacute bacterial endocarditis in five (1%). Actuarial long-term survival was 80% at 5 years and 71% at 8 years. Thromboembolism occurred in 34 patients (9.5%). The incidence of thromboembolism per 100 patient-years for patients receiving no anticoagulants was 5.4; antiplatelet agents, 2.9; and Coumadin (sodium warfarin), 2.6. Major thromboembolism was uncommon in patients on a regimen of sodium warfarin but major morbidity from bleeding was significant.