Forty-seven cases of quadricuspid semilunar valves which were autopsied were reviewed. The ratio of quadricuspid pulmonic valve to quadricuspid aortic valve was 5:1. Among the 35 patients with quadricuspid pulmonic valves, there were ten patients with clinical and pathologic evidence of coexisting congenital cardiac defects, eight of which resulted in severe cyanotic heart disease in infancy. In the remaining 25 patients the quadricuspid pulmonic valve was an incidental finding at autopsy. Three of the seven patients with quadricuspid aortic valves had aortic insufficiency, while the remaining four had no other clinical or pathologic evidence of congenital heart disease.