The purpose of this study was to determine the cause, onset, clinical outcome and treatment of aortic insufficiency developing during treatment of complex cardiac anomalies. Aortic insufficiency associated with ventricular septal defect is a well-recognized entity. Very few studies, in contrast, have addressed the development of aortic insufficiency in the presence of more complex cardiac anomalies. Ten patients were selected from two clinical centers. All patients were diagnosed with a major cardiac anomaly requiring surgical treatment. Each patient developed aortic insufficiency requiring a surgical treatment of the valve after correction or palliation of their cardiac defect. There were six males, and mean age for the series was 17 years (range 5.5 to 33 years). All patients were initially operated for repair (eight patients) or palliation (two patients) of their congenital anomaly. Five patients had tetralogy of Fallot, one had tetralogy associated with pulmonary atresia, and two patients had double outlet right ventricle, and two had complete transposition. The degree of aortic insufficiency, the amount of pulmonary stenosis present before the original procedure and the diameter of the aortic root measured before the aortic surgical procedure on the valve were assessed by angiography and echocardiography. The mean time between the last surgical procedure and the appearance of aortic regurgitation was three years, with a mean time between the last intervention and the aortic procedure of 7.3 years. The etiology of the insufficiency was explained by prolapse of an aortic leaflet in three patients. Four patients had annular dilation with central regurgitation, two patients had traumatic perforation of a leaflet, one patient had lesions consistent with endocarditis. Eight patients had dilation of the aortic root. Surgical procedures included five replacements of the aortic valve, three aortic valvoplasties, one aortic valvar replacement associated with a Glenn shunt, and one Bentall procedure. One patient died two months following an aortic valvar replacement. All patients were assessed by transthoracic echocardiography before discharged. The two main causes of aortic regurgitation, leaflet prolapse and annular dilation are age-related complications. Most patients had dilation of the aortic root from longstanding increases in aortic flow. Early repair of congenital anomalies may decrease these complications.