Mortality, major neurological handicaps--including mental retardation, cerebral palsy and epilepsy--educational subnormality and height at 14 years of age were studied by birth weight percentiles in a birth cohort of 12 000 children from northern Finland. Infant mortality was significantly higher below the mean -2 SD, 10th and 25th percentiles, than in the median class, from 25th to 75th percentiles, but mortality from one to 14 years only in the lowest weight class. Educational subnormality, including mental retardation +/- some other handicap, was highly significantly more frequent in all the percentile classes lower than the median class but showed no significant tendency to be less frequent in the percentiles over the median. It was also highly significantly more frequent among the preterm than the term infant. The number of children with a major neurological handicap but normal school performance did not vary significantly by birth weight percentiles or by gestational age. Height at 14 years increased significantly by birth weight percentiles. The height of the boys with birth weight mean - and +2 SD was nevertheless within the 25th-75th percentiles for height at 14 years in general, while the height of the girls came close to these percentile limits. The preterm infants were significantly shorter than the term infants at 14 years.