The morphologic features of 307 colorectal adenomas among 159 patients are reviewed. Most adenomas (66.4%) were located in the sigmoid colon and the rectum, and the percentage decreased proximally to the right colon. The 307 adenomas comprised 244 (79.5%) tubular, 41 (13.3%) tubulovillous, and 22 (7.2%) villous adenomas. The epithelial dysplasia was graded as mild in 260 (84.7%) adenomas, moderate in 33 (10.7%), and severe in 14 (4.6%). The percentage of severe dysplasia was greater in villous adenomas than in tubular adenomas (p less than 0.05) and correlated with the increasing size (greater than 5 mm) of the adenomas (p less than 0.01). The risk of metachronous adenomas could be evaluated among 56 patients, 34 men and 22 women with a history of removed adenoma(s). Fourteen of 56 patients (25%) with 6:1 male to female ratio developed 18 new adenomas, after an average of 34.3 months (range, from 12 to 88 months). Eleven of the 14 patients had multiple adenomas at the initial examination. In addition, a carcinoma of the rectum was found in one male patient. Of the 48 patients, 17 men and 31 women, operated on for colorectal cancer 16 patients (34%) with 1.3:1 male to female ratio had 40 new adenomas after an average of 51.8 months (range, 12 to 252 months) after the surgical excision of their carcinomas. One patient had a recurrent carcinoma at the site of the anastomosis 22 months after anterior resection of his carcinoma. Our data suggest that a history of colorectal carcinoma, multiple adenomas, and male sex predict a higher risk of having future colorectal tumours.