The presence of malformations in a population-based series of 181 children diagnosed with soft tissue sarcoma and in the majority of their parents and siblings was ascertained from family interviews and medical records. Five index children (2.8%) had serious anomalies, a figure not in excess of that derived from general population data. Fourteen siblings (4%) were affected, and higher rates of malformations were seen in siblings of female case children (P = 0.06) and siblings of children with visceral tumours (P = 0.03). There was no correlation between site of tumour in the index and specific organ system anomalies in the index or in their respective siblings. The survey indicated that there are unlikely to be strong associations between childhood soft tissue sarcoma and major malformations, a situation distinct from that found in Wilms' tumour.