BACKGROUND: Recent studies have revealed increased morbidity and mortality rates in term neonates without birth defects who were delivered before 39 weeks of completed gestation. We sought to determine if a similar association exists between gestational age at delivery and adverse outcomes in neonates with critical congenital heart disease, with particular interest in those born at 37 to 38 weeks' gestation. PATIENTS AND METHODS: We studied 971 consecutive neonates who had critical congenital heart disease and a known gestational age and were admitted to our cardiac ICU from 2002 through 2008. Gestational age was stratified into 5 groups: >41, 39 to 40, 37 to 38, 34 to 36, and <34 completed weeks. Multivariate logistic regression analyses were used to evaluate mortality and a composite morbidity variable. Multivariate Poisson regression was used to evaluate duration of ventilation, intensive care, and hospitalization. RESULTS: Compared with the referent group of neonates who were delivered at 39 to 40 completed weeks' gestation, neonates born at 37 to 38 weeks had increased mortality (6.9% vs 2.6%; adjusted P = .049) and morbidity (49.7% vs 39.7%; adjusted P = .02) rates and tended to require a longer duration of mechanical ventilation (adjusted P = .05). Patients born after 40 or before 37 weeks also had greater adjusted mortality rates, and those born before 37 weeks had increased morbidity rates and required more days of mechanical ventilation and intensive care. CONCLUSIONS: For neonates with critical congenital heart disease, delivery before 39 weeks' gestation is associated with greater mortality and morbidity rates and more resource use. With respect to neonatal mortality, the ideal gestational age for delivery of these patients may be 39 to 40 completed weeks.