BACKGROUND: In the PREVAIL study, enzalutamide significantly improved clinical outcomes versus placebo in patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC). OBJECTIVE: To evaluate long-term benefits and risks of enzalutamide in the final prespecified PREVAIL analysis. DESIGN, SETTING, AND PARTICIPANTS: We conducted a final 5-yr survival analysis of PREVAIL in men with chemotherapy-naïve mCRPC from the enzalutamide (n = 689) and placebo (n = 693) arms. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Predictors of the primary outcome of overall survival were estimated using the Kaplan-Meier method. Long-term adverse events over time were analyzed. RESULTS AND LIMITATIONS: At the 5-yr data cutoff, 1382 of 1717 (80%) men had died. Enzalutamide reduced the hazard of death by 17% (hazard ratio 0.83; 95% confidence interval [CI] 0.75-0.93; p < 0.001), despite 65%, 54%, and 43% of placebo-treated patients receiving subsequent docetaxel, abiraterone, and enzalutamide, respectively. Median overall survival was 36 mo (95% CI 34-38) in the enzalutamide arm versus 31 mo (95% CI 29-34) in the placebo arm, with a median follow-up of 69 mo. Prognostic modeling showed 5-yr survival rates of 42%, 24%, and 5% for low-, intermediate-, and high-risk groups, respectively. Greater degrees of confirmed prostate-specific antigen declines (≤3 mo) were associated with greater 5-yr survival. A higher incidence of fatal treatment-emergent adverse events was observed with enzalutamide (6.9% vs 3.8%), with an increase in fatal cardiovascular events (1.6% vs 0.4%). CONCLUSIONS: With >5 yr of follow-up, enzalutamide continued to demonstrate improved survival in patients with mCRPC despite crossover and multiple subsequent effective therapies, balanced against a slightly higher rate of fatal cardiovascular events. PREVAIL is registered on ClinicalTrials.gov as NCT01212991. PATIENT SUMMARY: We report a maintained long-term survival benefit with enzalutamide and risks with >5 yr of enzalutamide treatment and follow-up in men with metastatic prostate cancer, and identify groups of men with widely different outcomes based on clinical factors.