In a 4-year retrospective review of 801 pregnancies that resulted in the delivery of an infant weighing 4100 g (9 lb) or more, increased incidence of both maternal and perinatal complications was noted. There were no maternal deaths, and ther perinatal mortality rate was 0.49%. The second stage of labor was prolonged in 9.7% of primigravidas and in 2.2% of multiparas. Shoulder dystocia and perineal lacerations were related to increasing birthweight. Difficult deliveries resulting in clavicle fracture or brachial plexus injuries, and facial trauma contributed to the 11.4% perinatal morbidity rate. Asphyxia was observed in 7.7% and hypoglycemia in 5.2% of the neonates. Congenital anomalies (1.5%) were not increased in the large fetus group. Close surveillance for diabetes mellitus and anticipation of the potential complications associated with delivery of a large infant may reduce maternal and neonatal morbidity rates and maintain low mortality rates.