In unselected autopsies on 171 males and 109 females over 20 years of age in Tromsø, Northern Norway, adenomas of the colon and rectum were present in 40% of the males and 33% of the females. The frequency of adenomas increased with age in both sexes. Hyperplastic polyps were found in 20% of all cases with no variation in frequency with sex or age. Before the age of 65 most adenomas were located in the distal half of the large intestine in both sexes. After 65 years in males and 75 years in females the predilection site was shifted to the proximal half of the large intestine. The average size and grade of atypia of adenomas increased with age, but no significant difference in grade of atypia was found between the proximal and distal halves of the large intestine. The occurrence of adenomas was not associated with any of the common chronic diseases thought to be related to a western-style diet or to malignant or benign neoplasms elsewhere in the body. A significant association was found between the occurrence of adenoma and high body weight. The findings support the role of adenomas as precursors of colorectal carcinoma.