The clinical manifestations of Gardner's syndrome were studied in 280 patients from 11 families. Forty-five per cent of the patients at risk inherited the syndrome. Forty-one patients had carcinoma of the intestine develop, with only a 27 per cent survival rate for this type cancer. Eight per cent of the patients with the syndrome showed peritoneal fibrosis and fibrous tumors. They also had carcinomas of the ampulla of Vater, liver, bldder and ovary develop as well as osteogenic sarcoma. The patients without the syndrome had carcinomas of the pancreas and breast develop as well as melanoma and leukemia. Twelve of the 16 patients having had a colectomy and ileoproctostomy showed regression of the remaining polyps of the rectum.