Healthy adults completed smoking and alcohol consumption questionnaires before colonoscopies, which were performed because of occult blood in the stool or prior barium enema suggesting polyps. Subjects with adenomas at colonoscopy (n = 102) were compared with colonoscopy-negative controls (n = 89). In univariate analyses, age (p less than 0.05), male sex (p less than 0.005), cumulative smoking (p less than 0.0001), and cumulative beer consumption (p less than 0.005) were associated with adenomas. The association of smoking with adenomas was stronger in younger subjects. The association of beer with adenomas was stronger in older subjects. Logistic regression confirmed statistically significant associations of smoking (odds ratio for greater than 40 pack-years = 3.31; confidence intervals 1.41, 7.81) and beer consumption (odds ratio for greater than 40 beer-years = 2.64; confidence intervals 1.10, 6.32) with adenomas. These results suggest that smoking and beer consumption are independent risk factors for colonic adenomas.