As part of a longitudinal follow-up program a single case analysis of the history of 53 children with a birthweight of less than 1501 g, who had developed cerebral palsy, was performed. In 17 children (32%) a definite explanation for the neurological impairment and in another 17 (32%) at least a possible explanation could be found. In 19 of the 53 children (36%) the history was uneventful and did not offer a causal event. The common documentation in obstetric and pediatric case files left the cause of cerebral palsy undetected in one third of the cases.