One hundred sixty-one cases of DiGeorge syndrome (111 previously reported in which details concerning individual patients were given and 50 observed) were analyzed for occurrence and type of cardiovascular anomalies. Only 5 patients had a normal heart. Interrupted aortic arch type B was the major anomaly in 48 patients and persistent truncus arteriosus in 37. Therefore, in about half of the patients with DiGeorge syndrome the major anomaly was one that is rare. Conversely, of those patients with interrupted aortic arch, 68% had DiGeorge syndrome, as did 33% of all patients with truncus arteriosus. Although tetralogy of Fallot was also seen often in DiGeorge syndrome (10 patients), these cases represented less than 2% of the total number of cases of tetralogy of Fallot. Similarly, less than 1% of children with isolated ventricular septal defect or transposition of the great arteries had DiGeorge syndrome. The primary cardiovascular anomaly always involved the aortic arch system or the arterial pole of the heart. Recent studies show that neural crest cells play a crucial role in development of pharyngeal (bronchial) pouch derivatives, e.g., thymus and parathyroid glands, as well as the aortic arches and the truncoconal part of the heart. These studies and present observations support the view that DiGeorge syndrome and the associated cardiovascular anomalies are due to an abnormal developmental process involving the neural crest. Curiously, no instances of aortopulmonary septal defect or anomalous origin of a pulmonary artery from the ascending aorta (hemitruncus) have been associated with DiGeorge syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)