Computed tomography (CT) of the brain has been used to evaluate potential etiologies of hemiplegic cerebral palsy in a population-based group of 28 children born preterm, in whom an obvious postnatal cause of hemiplegia could be excluded. The CT findings were classified according to a system so constructed to reflect the phase of brain maturation during which the insult causing hemiplegia likely had occurred. We found that 50% had evidence of periventricular leukomalacia the lesion typical of hypoxic-ischemic injury to the immature brain. However, it was not possible, neither from the CT scans nor from retrospective review of available clinical data, to date the injury more precisely to the pre- or perinatal period. Analysis of CT findings further showed that 18% of the children had cerebral maldevelopment, indicating an injury during early fetal life as the cause of hemiplegia, earlier than clinically suspected. The CT scans were normal in 25% of the children. It is concluded that the objective information obtained by studying the morphology of brain lesions using CT provides important information in addition to clinical data, and should be integrated with clinical assessment when attempts are being made to evaluate the etiology of cerebral palsy in children.