The relation between inflammatory bowel disease (IBD) and colorectal cancer (CRC) is not clearly defined. Some investigators suggest that patients with extensive colitis have a genetic predisposition to CRC and that long-standing inflammation is not of primary importance in the promotion of cancer. We have assessed any increased risk of colon cancer in the relatives of IBD patients. We studied the prevalence of malignancy in the relatives of 251 IBD patients [198 ulcerative colitis (UC); 53 Crohn's disease of the colon (CDC)] and 251 orthopedic patients (ORTHO) as controls. In all patients (UC, CDC) as well as in controls (ORTHO) the prevalence of colon, extracolic digestive and extradigestive malignant tumors in the first-degree relatives was evaluated. We found no significant difference in the number of colorectal tumors or of tumors of any other kind in the diverse group of relatives of patients with IBD and ORTHO patients. Our data do not point to the existence of hereditary factors linking UC or CDC to CRC.