PURPOSE: Ipilimumab and radiation therapy (RT) are standard treatments for advanced melanoma; preclinical models suggest the potential for synergy. However, limited clinical information exists regarding safety and optimal timing of the combination. METHODS AND MATERIALS: We reviewed the records of consecutive patients with unresectable stage 3 or 4 melanoma treated with ipilimumab. Patients were categorized as having received RT or not. Differences were estimated between these 2 cohorts. RESULTS: We identified 88 patients treated with ipilimumab. At baseline, the ipilimumab-plus-RT group (n=44) had more unfavorable characteristics. Despite this, overall survival, progression-free survival, and both immune-related and non-immune-related toxicity were not statistically different (P=.67). Patients who received ipilimumab before RT had an increased duration of irradiated tumor response compared with patients receiving ipilimumab after RT (74.7% vs 44.8% at 12 months; P=.01, log-rank test). In addition, patients receiving ablative RT had non-statistically significantly improved median overall survival (19.6 vs 10.2 months), as well as 6-month (95.1% vs 72.7%) and 12-month (79.7% vs 48.5%) survival rates, compared with those treated with conventionally fractionated RT. CONCLUSIONS: We found that both ablative and conventionally fractionated RT can be safely administered with ipilimumab without a clinically apparent increase in toxicity. Patients who received ipilimumab before RT had an increased duration of irradiated tumor response.