Single-agent PD-1 blockade exhibits limited efficacy in epithelial ovarian cancer (EOC). We evaluated ipilimumab plus nivolumab compared with nivolumab alone in women with persistent or recurrent EOC.Eligibility criteria included measurable disease, 1-3 prior regimens, and platinum-free interval (PFI) < 12 months. Participants were randomly allocated to intravenous nivolumab (every 2 weeks) or induction with nivolumab plus ipilimumab for 4 doses (every 3 weeks), followed by every-2-week maintenance nivolumab for a maximum of 42 doses. The primary null hypothesis was equal probability of objective response within 6 months of random allocation in each arm.One hundred patients were allocated to receive either nivolumab (n = 49), or nivolumab plus ipilimumab (n = 51), with PFI of < 6 months in 62%. Six (12.2%) responses occurred within 6 months in the nivolumab group and 16 (31.4%) in the nivolumab plus ipilimumab group (odds ratio, 3.28; 85% CI, 1.54 to infinity; P = .034). The median progression-free survival (PFS) was 2 and 3.9 months in the nivolumab and nivolumab plus ipilimumab groups, respectively, with a PFI-stratified hazard ratio of 0.53 (95% CI, 0.34 to 0.82); the respective hazard ratio for death was 0.79 (95% CI, 0.44 to 1.42). Grade ≥ 3 related adverse events occurred in 33% of patients in the nivolumab group and 49% in the combination group, with no treatment-related deaths. PD-L1 expression was not significantly associated with response in either treatment group.Compared with nivolumab alone, the combination of nivolumab and ipilimumab in EOC resulted in superior response rate and longer, albeit limited, PFS, with toxicity of the combination regimen comparable to prior reports. Additional combination studies to enhance durability of the dual regimen are warranted.