OBJECTIVES: A within-trial analysis examined the cost-effectiveness of dutasteride as a chemoprevention compared with placebo, by analyzing the resource use incurred by men in Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial. METHODS: REDUCE was a 4-year, randomized, double-blind, placebo-controlled, parallel-group trial to compare the efficacy and safety of dutasteride 0.5 mg daily with placebo for chemoprevention in men at increased risk for prostate cancer. Resource use data was prospectively collected and included drugs, procedures, outpatient visits, and inpatient visits in general and those associated with related conditions such as hematuria, hematospermia, acute urinary retention, urinary tract infection, benign prostatic hyperplasia, and prostate cancer. Unit costs from standard costing sources were applied to resource use incurred during the trial. Quality-adjusted life-years (QALYs) were calculated on the basis of men being healthy and having BPH, prostate cancer, and adverse events. Utilities were obtained from the published literature. Incremental costs per QALY were calculated. Bootstrap analyses, to derive cost-effectiveness acceptability curves, were performed. The analysis was performed from the perspective of a United States healthcare payer. RESULTS: Men using dutasteride incurred a mean cost of $6,610 (including cost of dutasteride) whereas men in the placebo group incurred a mean cost of $3,177 over the 4-year period of the trial. Men using dutasteride accrued 0.13 more QALYs than men on placebo (3.26 vs. 3.13). As a result, the use of dutasteride as a chemoprevention was cost-effective (incremental cost per QALY