Background: Colorectal cancer is common worldwide and chemoprevention has the potential of reducing the number of individuals who may suffer and perish from this disease. Methods: A randomized placebo controlled pilot study in colorectal cancer patients was performed using calcium carbonate as the test agent in a multi-institutional oncology study group. Results: Two hundred twenty volunteers were randomized in the study. The primary goals of compliance, accrual, and toxicity monitoring are presented. Presence of multiple adenomas at study entry and subsequent development of metachronous adenomas were recorded and found to be associated with synchronous adenomas. The secondary endpoint of recurrent adenomas indicated lower rates of new adenoma in the volunteers randomized to the calcium group. Conclusion: This pilot study indicates the feasibility of enrolling survivors of colorectal cancer as study volunteers in a colorectal neoplasm chemoprevention clinical trial and oral calcium continues to be a potentially effective drug in reducing colorectal adenomas. © 2011 Elsevier Inc. All rights reserved.