Two hundred fifty-one patients with Down syndrome and congenital heart disease was based on clinical (41%), catheterization (38%), surgical (11%), or autopsy data (10%). The most common lesions were endocardial cushion defect (43%), ventricular septal defect (32%), secundum atrial septal defect (10%), tetralogy of Fallot (6%), and isolated patent ductus arteriosus (4%). Thirty percent had multiple cardiac defects. The most common associated lesions were patent ductus arteriosus (16%) and pulmonic stenosis (9%). Twenty-five percent of the patients uncerwent cardiac surgery. Motality in the 68 patients undergoing surgery was 26% for open heart procedures and 11% for closed heart surgery. In 32% of nonsurgically treated patients with large left-to-right shunts, irreversible pulmonary vascular disease developed. Improved medical and surgical care have decreased morbidity and mortality in these patients in recent years.