Purpose There is evidence from nonrandomized studies that a proportion of ipilimumab-treated patients with advanced melanoma experience long-term survival. To demonstrate a long-term survival benefit with ipilimumab, we evaluated the 5-year survival rates of patients treated in a randomized, controlled phase III trial. Patients and Methods A milestone survival analysis was conducted to capture the 5-year survival rate of treatment-naive patients with advanced melanoma who received ipilimumab in a phase III trial. Patients were randomly assigned 1:1 to receive ipilimumab at 10 mg/kg plus dacarbazine (n = 250) or placebo plus dacarbazine (n = 252) at weeks 1, 4, 7, and 10 followed by dacarbazine alone every 3 weeks through week 22. Eligible patients could receive maintenance ipilimumab or placebo every 12 weeks beginning at week 24. A safety analysis was conducted on patients who survived at least 5 years and continued to receive ipilimumab as maintenance therapy. Results The 5-year survival rate was 18.2% (95% CI, 13.6% to 23.4%) for patients treated with ipilimumab plus dacarbazine versus 8.8% (95% CI, 5.7% to 12.8%) for patients treated with placebo plus dacarbazine (P = .002). A plateau in the survival curve began at approximately 3 years. In patients who survived at least 5 years and continued to receive ipilimumab, grade 3 or 4 immune-related adverse events were observed exclusively in the skin. Conclusion The additional survival benefit of ipilimumab plus dacarbazine is maintained with twice as many patients alive at 5 years compared with those who initially received placebo plus dacarbazine. These results demonstrate a durable survival benefit with ipilimumab in advanced melanoma.