The association between calcium intake and the risk of colorectal neoplasia remains controversial. This analysis prospectively investigated the association between dietary and supplemental calcium intake and recurrent colorectal adenomas. Participants were part of a multicenter, randomized clinical trial of antioxidant vitamins. The study endpoints were adenomas detected between surveillance colonoscopies conducted at approximately 1 year and 4 years after study entry. Baseline intake of energy-adjusted calcium derived from a food frequency questionnaire was used as the main exposure of interest. Calcium supplement use was assessed by semiannual questionnaires. Logistic regression was used to compute odds ratios and 95% confidence limits, and Poisson regression was used to estimate rate ratios. Subjects in the fifth quintile of dietary calcium had an adjusted odds ratio of 0.72 (95% confidence interval, 0.43-1.22) compared to those in the lowest quintile. Investigation of the numbers of adenomas yielded stronger findings: the rate ratio for the fifth quintile versus the first was 0.63 (95% confidence interval, 0.39-1.02). Dietary calcium seemed to have a greater effect among individuals with a high-fat diet than among those with a low-fat diet; however, the interaction was not statistically significant. Use of calcium supplements was not related to adenoma recurrence. These results suggest that a high calcium intake may be associated with a reduction in risk of recurrent adenomas, especially among individuals on a high-fat diet.