We have studied the epidemiology of colorectal cancer in Asturias. We have collected 850 cases of colonic and rectal cancer, diagnosed from 1977 to 1981 (470 males and 380 females). The incidence was 17.13 per 100,000 for males and 13.08 per 100,000 for females. The incidence adjusted for the age was 12.32 (males) and 7.95 (females). The average age was 63.68 and 64.06, for females and males, respectively. The more frequent localization were rectum, sigmoid colon and cecum. Two hundred and sixty two patients lived in rural areas and 588 in urban areas. In 57.9% of the cases of blood group was A. The most common presenting symptoms were abdominal pain and blood in the feces. 69.9% of the tumors were Dukes' type C. The treatment was elective surgery in 693 cases. Five years after surgery the survival rates were 44.1% for tumors type C, and 68.5% for tumors type B. During the period of present study underlines the importance of the programs directed to the early diagnosis of high risk groups, as an efficient secondary prevention of the colorectal carcinoma.