From 1976 to 1980, 1034 infants with birth weights of 500-2000 g were cared for in the neonatal medical unit; 724 were discharged. Twenty (2.8%) subsequently died and 654 (90.3%) were followed up at a median age of 3 years 3 months. Fifty five (7.6%) survivors had major neurodevelopmental handicaps not attributable to congenital anomalies. Increasing prevalence of major handicap was found with decreasing birth weight and gestation. Children with birth weights of less than 1251 g had a higher incidence of all major disabilities. Handicapped children with a birth weight less than 1251 g were more likely to have blindness, deafness, multiple disabilities, and more severe cerebral palsy. There were 146 (20.2%) children with minor disabilities: neurological impairments (n = 11), borderline results on psychometric testing (n = 18), visual impairments (n = 52), hearing impairments (n = 40), and speech impairments (n = 71). Children weighing less than 1251 g at birth had a higher incidence of minor visual and hearing impairments. In 389 children the mean Griffiths quotient was 101.6 (SD 17.2) (range 50-147), and 158 children had a mean Wechsler preschool and primary intelligence quotient of 101.8 (13.2) (range 56-127): these quotients did not vary with birth weight or gestation but did vary with socioeconomic group, schooling, and family structure. During the study period an improving prognosis in terms of both survival and handicap was observed in children weighing less than 1251 g at birth.