Mothers of a population-based series of young adults with bone and soft tissue sarcoma were traced and their cancer risks estimated. No overall excess of cancers compared with expected numbers calculated from population rates was seen but mothers of patients with synovial sarcoma had significantly more cancers than expected and this was accounted for mainly by an excess of breast cancer. In addition there were strong indications that a proportion of cases were members of families with inherited cancer-prone syndromes, in particular with neurofibromatosis or with the Li Fraumeni cancer family syndrome.