A bicuspid aortic valve is found in approximately 2 % of the population. The data in the literature concerning the incidence of clinical manifestations are inconsistent, and a detailed comparison with patients with tricuspid aortic valve is not yet available. We analyzed the clinical manifestations and demographic data of patients with bicuspid and tricuspid aortic valves who underwent an operation on the aortic valve and/or the ascending aorta over a five-year period. The subjects were 2570 adult patients, of whom 555 (21.6 %) had a bicuspid aortic valve. The patients with a bicuspid aortic valve were, on average, 10 years younger at surgery than those with a tricuspid aortic valve (57.0 +/- 13.1 vs. 66.4 +/- 11.8 years, P < 0.0001). The spectrum of diseases necessitating aortic valve surgery was the same in both groups of patients. An increased diameter of the ascending aorta > or = 4.5 cm was seen significantly more often in patients with bicuspid aortic valve (22.7 % vs. 5.5 %, P < 0.0001). We conclude that there are important differences in clinical manifestations between patients with bicuspid and tricuspid aortic valves, so that patients with bicuspid valve need special attention.