Hemiplegic cerebral palsy (CP) was studied in a retrospective population-based series of 169 cases from the South-western Swedish health care region covering the birth years 1969-78. The purpose was to analyse the prevalence, aetiology and neuro-developmental outcome in children born preterm and at term, and to correlate pathogenetic periods, aetiological factors and clinical parameters to neuroradiology. The prevalence at the ages 6-15 years was 0.66 per 1000. Postnatally acquired hemiplegia, mainly postinfectious, iatrogenic or posttraumatic, constituted 11%. Among term children with congenital hemiplegia (pre and perinatally derived) the aetiology was considered prenatal, mainly circulatory brain lesions and maldevelopments, in 42%, combined pre and perinatal in 9%, perinatal (cerebral haemorrhage, hypoxia) in 16% and untraceable in 34%. The corresponding distribution among preterm children was 29%, 47%, 25% and 6%, respectively. The rate of preterm birth among congenital cases was 24%. Birth asphyxia was shown to be a poor indicator of pathogenetic period, whereas a cascade of postpartum complications suggested perinatal brain damage. Clinical follow-up of 152 children revealed that 50% had mild, 31% moderate and 19% severe motor dysfunction. Stereognostic sense was impaired in 44% of the children (astereognosia in 20%). Additional impairments (mental retardation, epilepsy, impaired vision, hearing and speech, severe behavioural/perceptual problems) were present in 42%. Term children with congenital hemiplegia tended to be more severely affected than preterm children. The resulting total handicap was considered mild in 40%, moderate in 44% and severe in 16%. The prevalence of severe total handicap was highest among postnatal cases. Computerised tomography (CT), performed in 109 congenital cases, was normal in 26%, showed unilateral ventricular enlargement in 36% and revealed cortical/subcortical cavities in 20%. In the remaining 18% CT findings were classified as "other". With the classification so far used, correlations between CT findings and aetiologies were unsatisfactory and disappointing. In contrast, CT findings showed a strong correlation with clinical degree of severity and magnitude of associated handicap. As a rule, normal CT implied mild disability and unilateral ventricular enlargement moderate, whereas cortical/subcortical cavities were frequently associated with severe handicap, including mental retardation and epilepsy.