About half of the carcinomas and polyps of the large intestine is placed in the descendent colon and in the sigma, where most frequently the diverticula are found. Literature refers to them as varying percentage of association diverticulosis-carcinoma between 2 to 8 percent. The increase of the frequency of neoplasms and diverticula in the same population classes may indicate common factors in their development. The study includes 1149 cases of colo-rectal neoplasms examined in the Department of Scienze Chirurgiche--University of Siena, from january 1981 to december 1993. The association of carcinomas and diverticula has been found in 8.96% of the cases (103 pts) and the tumours with stenosis in 59,2% of the cases. The colonoscopy is very important for a more precise differential diagnosis especially in occlusive forms, in which a multiple biopsy is indispensable. Referring to the data of literature, the authors consider that patients with symptomatic diverticular disease have a major general risk for cancer of the large intestine; the existence of certain common symptoms in either disease (especially the bleeding) may not exclude the presence of a tumor in patients with diverticular disease.