The purpose of this study was to examine the long-term growth and developmental outcome of infants undergoing heart transplantation. We studied weight, length, and head circumference from birth to 12 months after surgery in 110 infant recipients less than 6 months of age. Forty-eight early transplant recipients (0 to 30 days) were compared with 62 late transplant recipients (31 to 180 days). Late transplant recipients showed less growth in all parameters at the time of transplant. However, by 6 months after transplantation, there were no differences between the two groups. Growth in 20 infants, now 3 to 7 years old, appears normal. Neurodevelopmental outcome was evaluated prospectively in 57 infants. Four months after transplantation, 11 infants (19%) had abnormal neurologic examinations, with generalized hypotonia (64%) being the most common finding. The Bayley Scale of Infant Development was administered to 48 of 57 infants. The Mental Developmental Index averaged 87 (+/- 21) and the Psychomotor Developmental Index averaged 90 (+/- 21). Of 140 infants who have undergone heart transplantation, transient postoperative seizures occurred in 23 survivors (21%) and 10 nonsurvivors (33%). Our findings suggest that growth, neurologic outcome, and development are normal in the majority of infants who undergo transplantation before 6 months of age.