Between 1962 and 1979, 14 patients with complete atrioventricular canal and tetralogy of Fallot underwent repair of both anomalies. The ages of the patients ranged from 1 to 12 years. Six patients had Down's syndrome. Five of the 14 had one or more previous systemic-pulmonary artery shunts. The correct diagnosis was established preoperatively in 11 of the patients. The ventricular septal defect, with its large anterior subaortic extension, was repaired by a combined atrial and right ventricular approach in five patients and by an atrial approach alone in nine. Outflow tract reconstruction (transannular patch) was performed in seven patients, without affecting the surgical mortality. Mortality was higher with associated Down's syndrome, but no significantly so (p = 0.1), and was related to age less than 4 years (p = 0.04). The presence of complete atrioventricular canal should be considered in patients with tetralogy of Fallot, especially those having Down's syndrome, electrocardiographic superior-axis deviation, and vectorcardiographic counterclockwise frontal QRS loop. This diagnosis can be confirmed preoperatively by right and left ventricular angiocardiography and two-dimensional echocardiography. The overall risk of repair has been high (29% early, 14% late mortality), but the mortality has been reduced to 17% during the last 10 years. No deaths have occurred in five recent patients who underwent closure of the ventricular septal defect by a combined atrial and ventricular approach.