To investigate the role played by chronic intrauterine insult in the genesis of neurodevelopmental disability (NDD), three analyses have been applied to a case-controlled study which compared a population of children with NDD with a control group of normally developed children. In the first analysis, average birthweight in children with NDD was 3138 g (SD 592) which was significantly less than in normally developed children, 3280 g (SD 491) (P less than 0.0005). After correction for confounding factors, birthweight-for-gestation (Z score) remained lower in children with NDD (-0.42) than normal children (-0.21) (P less than 0.0025). In the second analysis the fetal growth achievement of children, who had NDD after the prenatal complications, severe hypertension, unclassified antepartum haemorrhage and preterm uterine activity, was significantly less (Z score, -0.76) than children who were normally developed after the same maternal prenatal complications (Z score, -0.37) (P less than 0.03). In the third analysis, a risk analysis to assess the relative importance of fetal growth achievement and prenatal complications in the genesis of NDD suggested that the latter was the dominant factor. These data are consistent with the hypothesis that prenatal complications, severe enough to retard fetal growth, can compromise fetal brain development and make an important contribution to NDD.