From August 1983 to December 1985, 2352 radiological examinations of the colon were performed in the Radiology Department of Università Cattolica del Sacro Cuore of Rome. From this group a sample of 222 patients was analyzed. They included 111 patients with colonic polyps and 111 with cancer. These cases were carefully examined, in terms of age, frequency of this pathology according to sex, symptom-illness rate, and the radiological data were compared with the endoscopic and histological findings. The data were processed using a computerized program. A critical correlation of the data obtained revealed that: 1) The surest symptom of colon carcinoma is blood in faeces with or without changes in defaecation frequency. Nor should isolated bowel disorders be ignored ("irritated" colon due to organic injuries). 2) The diagnostic accuracy of double contrast enema is very close to that of endoscopy, provided that intestinal cleaning is adequate (this in fact is an important aspect of the examination). 3) The mean age of patients in this group is high and cancer is more common than polyps. This seems to be due to the back of a complete diagnostic sequence, in which radiology has a specific and important role.