Family cancer syndrome: a study of the kindred of a man with osteogenic sarcoma of the mandible. Several familial cancer syndromes have been identified. The syndrome of sarcomas, breast cancer and other neoplasms, known as Li-Fraumeni syndrome, is characterized by several different neoplasms presenting at young ages with autosomal dominant transmission and a high incidence of second primaries. In this paper, we studied six generations (51 people) of the family of a 24-year-old man with osteogenic sarcoma of the mandible. Twelve malignancies in 11 people, including several rare tumors, were revealed. Mean age of presentation was 24 years old. Nine of the 11 patients died of disease. One developed a second primary. Two tumors presented in the head and neck. Transmission was autosomal dominant. The karyotypes of two family members were normal. Identification of Li-Fraumeni syndrome in a family is important in determining appropriate follow-up for the patient and family. Such families are models for studying carcinogenesis. 