Ninety cases of familial multiple polyposis associated with soft-tissue and hardtissue tumors were analyzed. The results led to the conclusion that, in familial multiple polyposis, one at least of the many polyps of the large intestine will ultimately become malignant if not removed. In the Peutz-Jeghers syndrome, on the other hand, the polyps in either small or large intestine rarely become carcinomatous, and no reports have been found of metastasis or death from such malignancy. It is established that there is a familial association, perhaps a genetic relationship, of multiple polyposis with desmoid tumors, epidermoid cysts, and exostoses or osteomas. These concomitant abnormalities, if recognized, may aid in diagnosis and treatment of familial multiple polyposis.