In a study of 41 surgically removed colorectal adenomas of unselected size, the dysplasia was graded as mild in 9, as moderate in 22, and severe in 10 cases. Twenty-four of the lesions were classified as tubular adenomas and 17 as tubulo-villous. The presence of O-acylated sialic mucin was for each of the adenomas assessed as normal (19 cases), intermediate (13 cases) or absent (9 cases). The absence of O-acylated mucin was in the present study found to be highly predictive for severe dysplasia (89%). The morphometric measurements of epithelial structures showed that nuclear shape factor and nuclear stratification index were most significantly related to the grades of dysplasia. In a multivariate analysis, the grading of O-cylated sialic mucin most significantly contributed to the grade of dysplasia, and to a lesser degree, nuclear shape factor and nuclear stratification index. The presence of villous elements and the size of the adenomas had no independent influence on the grade of dysplasia in this statistical analysis.