Statins are widely prescribed for cardiovascular disease prevention and also commonly used in patients at high risk for colorectal cancer. We report the results of a planned secondary analysis of the relationship between statin use and colorectal adenoma risk in a large chemoprevention trial. The Adenoma Prevention with Celecoxib (APC) trial randomized 2,035 adenoma patients to receive placebo (679 patients), 200 mg celecoxib twice daily (bid; 685 patients), or 400 mg celecoxib bid (671 patients). The study collected complete medical history and medication use data and performed colonoscopic surveillance to 5 years after study enrollment. The effects of statin use on newly detected adenomas and cardiovascular adverse events were analyzed as time-dependent variables by multivariable Cox regression. Statins were used by 36% (n = 730) of APC trial participants. When adjusted for covariates including cardioprotective aspirin use, age, and sex, participants on the placebo arm who used statins at any time had no benefit over 5 years compared with never users (risk ratio, 1.24; 95% confidence interval, 0.99-1.56; P = 0.065). Statin use for >3 years increased adenoma risk over 5 years (risk ratio, 1.39; 95% confidence interval, 1.04-1.86; P = 0.024). For all comparisons of patients treated with celecoxib, adenoma detection rates for statin users and nonusers were equivalent. Consistent with their use in patients at high risk, cardiovascular serious adverse events were more common among statin users. For patients at high risk of colorectal cancer, statins do not protect against colorectal neoplasms and may even increase the risk of developing colorectal adenomas.