BACKGROUND: Atezolizumab treatment improves survival, with manageable safety, in patients with previously treated advanced/metastatic non-small cell lung cancer. The global phase III/IV study TAIL (NCT03285763) was conducted to evaluate the safety and efficacy of atezolizumab monotherapy in a clinically diverse population of patients with previously treated non-small cell lung cancer, including those not eligible for pivotal trials. METHODS: Patients with stage IIIB/IV non-small cell lung cancer whose disease progressed after 1-2 lines of chemotherapy were eligible for this open-label, single-arm, multicenter study, including those with severe renal impairment, an Eastern Cooperative Oncology Group performance status of 2, prior anti-programmed death 1 (PD-1) therapy, and autoimmune disease. Atezolizumab was administered intravenously (1200 mg every 3 weeks). Coprimary endpoints were treatment-related serious adverse events and immune-related adverse events. RESULTS: 619 patients enrolled and 615 received atezolizumab. At data cutoff, the median follow-up was 12.6 months (95% CI 11.9 to 13.1). Treatment-related serious adverse events occurred in 7.8% and immune-related adverse events in 8.3% of all patients and as follows, respectively, in these subgroups: renal impairment (n=78), 11.5% and 12.8%; Eastern Cooperative Oncology Group performance status of 2 (n=61), 14.8% and 8.2%; prior anti-PD-1 therapy (n=39), 5.1% and 7.7%; and autoimmune disease (n=30), 6.7% and 10.0%. No new safety signals were reported. In the overall population, the median overall survival was 11.1 months (95% CI 8.9 to 12.9), the median progression-free survival was 2.7 months (95% CI 2.1 to 2.8) and the objective response rate was 11%. CONCLUSIONS: This study confirmed the benefit-risk profile of atezolizumab monotherapy in a clinically diverse population of patients with previously treated non-small cell lung cancer. These safety and efficacy outcomes may inform treatment decisions for patients generally excluded from checkpoint inhibitor trials.