A prospective study was carried out on 133 neurologically deviant infants, 205 with mild abnormalities and 230 normal newborns to compare behavioural and cognitive development with neonatal and nine-year-old neurological condition. Overtly handicapped children were excluded. Major determinants of school failure were the severity of minor neurological dysfunction (MND) and social class. Main risk factors for distractable and clumsy behaviour were MND classification and male sex; for troublesome behaviour male sex and interval complications after two years of age; and for timid behaviour, family adversity. Definite neonatal neurological deviancy contributed both directly and by its association with MND to problems in behaviour and scholastic abilities. Mild neonatal neurological abnormalities and adverse obstetrical events contributed only indirectly to behavioural and learning problems. Preterm birth (less than 34 weeks) was the sole obstetric variable directly related to some of the outcome variables. The difference between home and school perception of the children's behaviour is emphasized.