Background: CheckMate 171 (NCT02409368) is an open-label, multicentre, phase 2 trial of nivolumab in previously treated advanced squamous non-small cell lung cancer (NSCLC), conducted as part of a post-approval commitment to the European Medicines Agency (EMA). We report outcomes from this trial. Methods: Patients with Eastern Cooperative Oncology Group performance status (ECOG PS) 0e2 and disease progression during/after !1 systemic treatment (!1 being platinum-based chemotherapy) for advanced or metastatic disease were treated with nivolumab 3 mg/kg every 2 weeks until progression or unacceptable toxicity. The primary end-point was incidence of grade 3e4 treatment-related select adverse events (AEs). Other end-points included overall survival (OS) and safety. Results: Of 811 patients treated, 103 had ECOG PS 2; 278 were aged !70 years and 125 were !75 years of age. Minimum follow-up was~18 months. Safety was similar across populations; the most frequent grade 3e4 treatment-related select AEs in all treated patients were diarrhoea (1%), increased alanine aminotransferase (ALT, 1%), pneumonitis (0.7%), colitis (0.6%) and increased aspartate aminotransferase (AST, 0.5%). Median OS was similar in all treated patients and those aged !70 and !75: 10.0 months, 10.0 months and 11.2 months, respectively. Median OS was 5.2 months in patients with ECOG PS 2. Conclusion: These results suggest that nivolumab is well tolerated and active in patients with advanced, relapsed squamous NSCLC, including the elderly, with OS outcomes consistent with phase 3 data. In patients with ECOG PS 2, nivolumab had similar tolerability, but outcomes were worse, as expected in this difficult-to-treat, poor prognosis population. Clinical trial registration: NCT02409368.