Congenital defects and other disorders have been reported in association with malignant liver tumours. In order to assess their significance, a population-based survey was undertaken on children aged less than 15 years diagnosed with malignant liver tumours during the 30 years 1957-1986. The cases were identified from information collected by the West Midlands Regional Children's Tumour Registry. Pertinent data were extracted from their clinical records, and the original biopsy and any necropsy material were reviewed by a panel of three paediatric pathologists. Of the 50 eligible cases registered, eight were excluded because histology review showed that they had non-malignant conditions (3) or malignancies of extrahepatic origin (4) or because no pathological material was available (1). The diagnoses in the remaining 42 cases were hepatoblastoma (27), hepatocellular carcinoma (3), rhabdomyosarcoma (6), rhabdoid tumour (3) and yolk sac tumour (3). The incidence of primary malignant liver tumours was 1.20 per 10(6) person years and that of the hepatoblastoma sub-group was 0.77 (average childhood population of the West Midlands for the time period being 1,166,500). The presenting clinical, radiological and biochemical features were similar to those reported in other series and the ethnic and social class distributions were unremarkable compared with the local population. Congenital defects or other possibly related features were present in nine (21%) patients. Our results, taken with other reports, suggest that hepatoblastoma is a malignant tumour related to maldevelopment, possibly associated with 11p or 5q mutations, whereas hepatocellular carcinoma is more usually a complication of metabolic and other disorders which lead to cirrhosis.