In recent years, several accounts have reported a proximal migration of colorectal cancer. To determine the experience at the Jewish General Hospital in Montreal, 1044 cases of large-bowel cancer that presented between the years 1955 and 1978 were analyzed. The colon was arbitrarily divided into five anatomic regions, and the distribution of cancer in each region for each of eight three-year periods was calculated. An increase in right-sided lesions occurred from 15.6 per cent in the first three-year period to 37.6 per cent in the final three-year period (P less than 0.01). No significant change occurred in transverse and left-colon lesions. An increase in sigmoid carcinomas occurred from 14 per cent to 35 per cent (P less than 0.01). A dramatic decrease in rectal carcinoma from 53 per cent to 2.1 per cent occurred (p less than 0.001). These findings imply that methods for the early detection and screening of large-bowel carcinoma should be directed at the entire colon rather than the distal 25 cm.