The relation of colorectal carcinoma and adenomatous polyps was studied retrospectively in 72 patients. Severe dysplasia was found in 47.8% and malignant transformation in 18.2% of the patients with adenomatous polyps and coincidental colorectal carcinoma. The incidence decreased to 21.4% and 7.1%, respectively, in patients with adenomatous polyps only. This difference between the two groups constitutes indirect evidence of malignant potential of adenomatous polyps associated with colorectal carcinoma. Moreover, when severe dysplasia of an adenomatous polyp is found, the patient should be carefully examined for synchronous colorectal carcinoma.