A prospective study of infants weighing less than 800 g at birth and cared for in a single neonatal intensive care unit between 1977 and 1980 was conducted. Neonatal mortality was 80%; neurodevelopmental outcome was assessed in 16 of the 18 survivors. Mean birth weight for these 16 was 730 g; mean gestational age was 26 weeks. Perinatal asphyxia, respiratory distress, apnea, mechanical ventilation, and chronic pulmonary disease were commonplace. Symptomatic intracranial hemorrhage, seizures, sepsis, or meningitis did not occur in survivors. Of the 16 infants, 13 (81%), including all three with birth weight less than 700 g, were without major CNS handicaps and were developing appropriately at 6 months to 3 years of age. Only one of the 16 had clearly subnormal mental development. None had a major visual or hearing impairment. Apgar scores at one and five minutes were significantly related to outcome; apnea, mechanical ventilation, and chronic pulmonary disease were not. These data suggest that a remarkably hopeful outcome is possible for the few survivors of extremely low birth weight.