Combined treatment with anti-PD-1 and anti-CTLA-4 antibodies has shown superiority over chemotherapy in patients with advanced non-small-cell lung cancer (NSCLC), but data for older patients (aged ≥70 years) with an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 or those with an ECOG performance status of 2 are scarce. We aimed to test the superiority of the PD-1 antibody nivolumab and the CTLA-4 antibody ipilimumab over platinum-based doublet chemotherapy as first-line treatment in patients with NSCLC aged 70 years or older or with an ECOG performance status of 2. This open-label, multicentre, randomised, controlled, phase 3 trial was done at 30 hospitals and cancer centres in France. Eligible patients had stage IV histologically proven NSCLC, with no known oncogenic alterations, and were either aged 70 years or older with ECOG performance status of 0-2 or younger than 70 years with an ECOG performance status of 2. Patients were randomly assigned (1:1) centrally, using a computer-generated algorithm stratified by age (<70 vs ≥70 years), ECOG performance status (0-1 vs 2), and histology (squamous vs non-squamous) to receive nivolumab plus ipilimumab or platinum-based doublet chemotherapy (carboplatin [area under the curve ≤700 mg] plus pemetrexed [500 mg/m2 intravenous infusion every 3 weeks] or carboplatin [on day 1; area under the curve ≤700 mg] plus paclitaxel [90 mg/m2 as intravenous infusion on days 1, 5, and 15, every 4 weeks]). The primary endpoint was overall survival; secondary endpoints included progression-free survival and safety. All efficacy analyses were performed in the intention-to-treat population, which included all randomly assigned patients. Safety was analysed in the safety analysis set, which included all randomly assigned patients who received at least one dose of study treatment and who had at least one safety follow-up. The trial is registered with ClinicalTrials.gov, NCT03351361. The trial was stopped early for futility on the basis of a pre-planned interim analysis after 33% of the expected events had occurred. Between Feb 12, 2018, and Dec 15, 2020, 217 patients were randomly assigned, of whom 216 patients were included in the final analysis, with 109 patients in the nivolumab plus ipilimumab group and 107 in the chemotherapy group; median age was 74 years (IQR 70-78). Median overall survival was 14·7 months (95% CI 8·0-19·7) in the nivolumab plus ipilimumab group and 9·9 months (7·7-12·3) in chemotherapy group (hazard ratio [HR] 0·85 [95% CI 0·62-1·16]). Among patients aged 70 years or older with an ECOG performance status of 0-1 (median age 76 years [IQR 73-79]), median overall survival was longer in the nivolumab plus ipilimumab group than the chemotherapy group: 22·6 months (95% CI 18·1-36·0) versus 11·8 months (8·9-20·5; HR 0·64 [95% CI 0·46-0·96]). Among patients with an ECOG performance status of 2 (median age 69 years [IQR 63-75]), median overall survival was 2·9 months (95% CI 1·4-4·8) in the nivolumab plus ipilimumab group versus 6·1 months (3·5-10·4) in the chemotherapy group (HR 1·32 [95% CI 0·82-2·11]). No new safety signals were reported. The most frequent grade 3 or worse adverse events were neutropenia (28 [27%] of 103 patients) in the chemotherapy group and endocrine disorders (five [5%] of 105 patients), cardiac disorders (ten [10%] patients), and gastrointestinal disorders (11 [11%] patients) in the nivolumab plus ipilimumab group. The study showed no benefit of nivolumab plus ipilimumab combination in the overall study population. As a result of early stopping, the trial was underpowered for primary and secondary endpoints; however, the finding of better survival with nivolumab plus ipilimumab compared with platinum doublet in the subgroup of older patients with NSCLC with an ECOG performance status of 0-1 warrants further study. Bristol-Myers Squibb.