The combined medical and surgical mortality rate for 125 infants with tetralogy of Fallot registered in the Baltimore-Washington Infant Study from 1981 to 1985 was 28% (mean age at follow-up for living infants, 40 months). Despite early diagnosis and successful early repair in many infants, significant risk factors for death included pulmonary atresia, major additional cardiac anomalies, major noncardiac malformations, low birth weight, and prematurity. There is a wide spectrum of severity, ranging from infants with isolated tetralogy and no risk factors who have an excellent prognosis to infants with three or more risk factors and a high probability of neonatal death. Further treatment advances will improve outcome in some, but not all, infants. A regional all-inclusive study of a specific cardiac defect can define research and treatment challenges not obvious from selected clinical series.