We conducted a case-control study to investigate the relation between dietary fiber, calcium, and total fat and the risk of colorectal adenomatous polyps. We used a food frequency questionnaire to assess the usual diet for 157 cases and 480 controls. In multivariate analyses, dietary fiber was inversely associated with risk of adenomatous polyps. The odds ratio (OR) for individuals in the highest vs the lowest quartile was 0.5 [95% confidence interval (CI) = 0.3-0.9]. We found an inverse association between dietary calcium and risk of adenomatous polyps, but the protective effect was present only for individuals in the fourth vs the first quartile (OR = 0.7; 95% CI = 0.3-1.3). Intake of total fat was positively associated with risk of adenomatous polyps, but we saw no consistent trend. Calcium intake appeared to modify the effect of total fat intake on the risk of adenomatous polyps.