Actuarial analysis based on postmortem examination of patients who had been treated nonsurgically for complete atrioventricular (A-V) canal defect shows that only 54% survive to 6 months of age, 35% to 12 months, 15% to 24 months, and 4% to 5 years of age. Our surgical experience since 1975 in 39 patients confirms the idea that primary repair is feasible in small infants. The highest risk of hospital death is when the operation is done in the early months of life; it falls to 17% by age 12 months. Between 1967 and October, 1976, the five-year survival rate among patients leaving the hospital alive after repair was 91%. The age-specific probability of "surgical cure" of patients operated upon for complete A-V canal (alive five years later with mean pulmonary artery pressure less than 25 mm Hg) is maximal at 73% when the operation is done at about 14 months of age. Urgent earlier repair is frequently necessitated by the life history of the disease.