The bicuspid aortic valve is the most frequent congenital cardiac malformation; it may be isolated or associated with other congenital heart disease. The present investigation consists of a study of bicuspid aortic valves in 1022 heart specimens belonging to the anatomical collection of the Institute of Pathological Anatomy of the University of Padua. A bicuspid aortic valve was observed in 95 specimens. It occurred as an isolated congenital cardiac defect in 28 cases, seven of which had spontaneous laceration of the aortic valve (aortic dissection). It was associated with other congenital cardiac malformations in 67 out of the remaining 994 specimens (6.7%), 41 of which (61.2%) showed obstruction of the aortic arch. The frequency of bicuspid aortic valve in specimens with complete transposition of great arteries was only 1%. Bicuspid aortic valve was particularly frequent in association with ventricular septal defect and was significantly more frequent in cases with (51.1%) than in cases without (20.5%) aortic arch obstruction (p < 0.001). There was no significant relationship between the occurrence of bicuspid aortic valves and left ventricular outflow tract obstructions or mitral valve malformations. The morphology of the pulmonary valve was also examined. Concurrence of a bicuspid aortic and pulmonary valve was detected in 11 specimens, five of these had trisomy-18. Our findings cast doubt on the assumption that altered fetal blood flow through the aortic valve may be the main factor producing the bicuspid condition. Indeed, they rather support the hypothesis that most bicuspid aortic valves are expressions of a developmental complex that affects the aortic arch and the wall of the ascending aorta as well as the aorta valve.