A family is presented in which the father and one of his children died, respectively, of pulmonary osteosarcoma and retroperitoneal liposarcoma; another child died of carcinoma of the colon with multiple polyposis; and a third has both a reticulum cell sarcoma and colonic polyps. The familial association of polyposis coli with extra-alimentary sarcomas has not previously been reported, and may be a variant of Gardner's syndrome (multiple polyposis with benign mesenchymal tumors). As in Gardner's syndrome, the familial pattern was consistent with autosomal dominant inheritance of a single mutant, highly penetrant, pleiotrophic gene. Phenotypic differences from Gardner's syndrome and familial polyposis suggest either that there was a separate gene or that the gene for one of these syndromes was expressed differently by modifiers segregating in this family. The development of fatal metastatic carcinoma of the colon in an 11-year-old boy appears to be the earliest recorded instance of this lesion