The purpose of this procurement is to conduct a clinical trial to determine efficacy and safety of celecoxib versus placebo in preventing the occurrences of newly detected colorectal adenomas in subjects at increased risk for colorectal carcinoma. In addition to incidence, other established risk factors will be evaluated for their association with occurrence of newly detected colorectal adenomas, including family history, and adenoma size, histopathologic grade, multiplicity, and location.