The congenital bicuspid aortic valve functions almost normally provided degeneration does not occur, but complications of infective endocarditis and calcification of the cusps with aging are indications for surgical intervention. We compared 22 cases with an incompetent bicuspid aortic valve (14 cases with stenosis and eight with regurgitation) with 96 cases of acquired tricuspid aortic valve (30 cases with stenosis and 66 with regurgitation) who were treated by aortic valve replacement (AVR) during the same period. Compared with the stenotic tricuspid aortic valve cases, the stenotic bicuspid aortic valve cases: 1) were older at AVR (59.3: 51.7 years, P < 0.05), 2) had a smaller diameter of preoperative valve orifice (6.9: 9.2 mm, P < 0.05), 3) had a smaller valve ring diameter (23.0: 24.3 mm, P < 0.05), 4) used artificial valves of almost identical size (22.0: 22.5), and 5) included no operative deaths (0: 10%). In contrast, compared with the tricuspid aortic valve cases with regurgitation, the bicuspid aortic valve cases with regurgitation: 1) were younger at AVR (39.5: 45.8 years), 2) had a higher incidence of infective endocarditis (62.5: 19.6%, P < 0.02) as a complication, and 3) showed a higher operative death rate (25.0: 6.1%), although this difference was not statistically significant. Suture repair of the incised portion of the aorta must be performed meticulously in patients with prominent poststenotic dilatation of the ascending aorta.