In 166 full term, small-for-gestational-age (FT-SGA), 53 preterm, appropriate-for-gestational-age (PT-AGA), 27 PT-SGA and 206 FT-AGA infants a neurological examination at the age of 6 years was carried out. Data were collected on behaviour and school achievement. Major and minor neurological abnormalities were more frequent in the three low birth weight groups, especially in the PT-SGA group. Multivariate analysis showed that the development of major and minor neurological abnormalities was explained by a varying set of risk factors, in which besides prematurity and growth retardation, neonatal neurological condition, social class, neonatal course and interval complications were preponderant. The results suggest a temporal difference in potentially harmful factors: for neurological handicap early in pregnancy, for minor neurological dysfunction (MND) the second half of gestation and the first 2 years of life. No striking behavioural differences were found between the three low birth weight groups and the FT-AGA group; behaviour was related to neonatal and follow-up neurological condition, sex, gestational age and birth weight to a limited extent only. Three (4%) of the preterms entered a special school (already at the age of 6). School achievement was mainly related to the present neurological condition and social class, which underlines the importance of the latter.