The presence of adenomas in 164 surgical specimens of the large intestine from 81 males and 83 females with colorectal carcinomas was compared with the presence of adenomas in a general necropsy population in northern Norway. In the group of patients with colorectal carcinomas the observed prevalence of single or multiple adenomas was 5.9 times higher than expected from the prevalence in the general necropsy population. The observed-to-expected ratios of all adenomas (4.7), adenomas with villous elements (4.6), adenomas with moderate or severe grades of dysplasia (4.9) and adenomas 10 mm or larger (5.5) were also higher in the surgical series. The study indicates that factors which initiate the growth of adenomas and, to a minor degree, factors which promote the growth of adenomas to a large size are more prevalent in individuals with colorectal carcinoma than in the necropsy population. Factors determining the presence of villous elements and the grades of dysplasia of adenomas seem to operate similarly in adenoma-bearing patients with and without colorectal carcinoma.