During the years from 1968 to 1984, at the First Department of Surgery in Olomouc, 10 patients with diffuse polyposis of the colon were treated. In 5 of them, a familial occurrence of polyposis was dealt with. In three of them, malignity developed. In five unfamilial polyposes, malignity occurred only once. In one patient, the occurrence of malignity was found present immediately with the first manifestation of the disease. In the other patients, it was after an interval of 3 to 17 years after the onset of the disease. Three patients died from generalization of the malignant process. In two of them, carcinoma developed in the remaining part of the colon, once after previous hemicolectomy and once after colectomy. One patient with an advanced disease died one year after proctocolectomy. Two other operated on patients survive after proctocolectomy 12 and 13 years. The other patients who had been operated on before the development of malignity are healthy. The choice of an adequate radicalintervention is of importance. Optimal is the performance of colectomy with ileorectal anastomosis and the regular endoscopic and bioptic follow-up of the stump of the intestine. When proctocolectomy is necessary, it is of advantage to apply Kock's continent ileostomy.