Safety and efficacy of the anti-PDL1 antibody atezolizumab versus chemotherapy were assessed in the phase III trial IMvigor211 in 931 patients with metastatic urothelial carcinoma who had progressed after platinum-based chemotherapy. In patients with PDL1 expression on ≥5% of tumour-infiltrating immune cells, overall survival did not differ between treatment arms (stratified HR 0.87, 95% CI 0.63–1.21), precluding further formal analysis. In the intention-to-treat population, grade 3–4 treatment-related adverse events were lower in the atezolizumab arm (20%) than in the chemotherapy arm (43%). Exploratory analysis of this population showed durable responses to atezolizumab.