In a register-based 19-year follow-up we studied the incidence rate of colorectal cancer in the Swedish 1960 census population. A total of 53,377 cases were identified: 28,003 men and 25,374 women. A U-shaped distribution of tumors in the large bowel was observed, with a minimum in the descending colon. Other findings were 1) An incidence gap between elderly men and women increasing with age and with distal direction in the large bowel; 2) An increase in the incidence of colorectal cancer with population density; 3) A higher incidence of colorectal cancer in the southwestern region than in the northern region and 4) A lower incidence of colon cancer among blue than among white collar workers and a lower incidence of colorectal cancer among never married men than among other men.