Preliminary trial results showed that enzalutamide significantly improved metastasis-free survival among men who had nonmetastatic, castration-resistant prostate cancer and rapidly increasing prostate-specific antigen (PSA) levels while taking androgen-deprivation therapy. Results from the final analysis of overall survival have not yet been reported. In this double-blind, phase 3 trial, men with nonmetastatic, castration-resistant prostate cancer (defined on the basis of conventional imaging and a PSA doubling time of ≤10 months) who were continuing to receive androgen-deprivation therapy were randomly assigned (in a 2:1 ratio) to receive enzalutamide at a dose of 160 mg or placebo once daily. Overall survival was assessed with a group sequential testing procedure and an O'Brien-Fleming-type alpha-spending function. As of October 15, 2019, a total of 288 of 933 patients (31%) in the enzalutamide group and 178 of 468 (38%) in the placebo group had died. Median overall survival was 67.0 months (95% confidence interval CI, 64.0 to not reached) in the enzalutamide group and 56.3 months (95% CI, 54.4 to 63.0) in the placebo group (hazard ratio for death, 0.73; 95% CI, 0.61 to 0.89; P = 0.001). The exposure-adjusted rate of adverse events of grade 3 or higher was 17 per 100 patient-years in the enzalutamide group and 20 per 100 patient-years in the placebo group. Adverse events in the enzalutamide group were consistent with those previously reported for enzalutamide; the most frequently reported events were fatigue and musculoskeletal events. Enzalutamide plus androgen-deprivation therapy resulted in longer median overall survival than placebo plus androgen-deprivation therapy among men with nonmetastatic, castration-resistant prostate cancer and a rapidly rising PSA level. The risk of death associated with enzalutamide was 27% lower than with placebo. Adverse events were consistent with the established safety profile of enzalutamide. (Funded by Pfizer and Astellas Pharma; PROSPER ClinicalTrials.gov number, NCT02003924.).