Behavioural and cognitive development at 12 years were studied in 172 children with and 174 children without minor neurological dysfunction (MND). MND could be differentiated into fine manipulative disability, co-ordination problems, hypotonia and choreiform dyskinesia. Fine manipulative disability related significantly to problems of cognition and behaviour; co-ordination problems to cognitive problems; and hypotonia and choreiform dyskinesia to behavioural problems, the former more than the latter. Socio-economic status and family adversity contributed to the risk for development of both cognitive and behavioural problems; gender did not. The onset of puberty seemed to change these relationships: follow-up is needed for definite conclusions.