A follow-up study at six and/or nine years of age was carried out on subpopulations of the three years cohort of the Groningen Perinatal Project. Neurological handicap and minor neurological dysfunction (MND) were associated with different sets of risk factors. The findings suggest a temporal difference in potentially harmful factors. At nine years of age two different kinds of MND could be distinguished, each of them related in a specific way to perinatal risk factors and behavioural and cognitive development. The finding that social factors, sex and present neurological condition of the child appeared to be more important than pre- and perinatal events for the development of learning and behavioural problems illustrates the complex aetiology of the latter.