Background Patients with advanced urothelial carcinoma have poor overall survival after platinum-containing chemotherapy and programmed cell death protein 1 (PD-1) or programmed death ligand 1 (PD-L1) inhibitor treatment. Methods We conducted a global, open-label, phase 3 trial of enfortumab vedotin for the treatment of patients with locally advanced or metastatic urothelial carcinoma who had previously received platinum-containing chemotherapy and had had disease progression during or after treatment with a PD-1 or PD-L1 inhibitor. Patients were randomly assigned in a 1:1 ratio to receive enfortumab vedotin (at a dose of 1.25 mg per kilogram of body weight on days 1, 8, and 15 of a 28-day cycle) or investigator-chosen chemotherapy (standard docetaxel, paclitaxel, or vinflunine), administered on day 1 of a 21-day cycle. The primary end point was overall survival. Results A total of 608 patients underwent randomization; 301 were assigned to receive enfortumab vedotin and 307 to receive chemotherapy. As of July 15, 2020, a total of 301 deaths had occurred (134 in the enfortumab vedotin group and 167 in the chemotherapy group). At the prespecified interim analysis, the median follow-up was 11.1 months. Overall survival was longer in the enfortumab vedotin group than in the chemotherapy group (median overall survival, 12.88 vs. 8.97 months; hazard ratio for death, 0.70; 95% confidence interval [CI], 0.56 to 0.89; P=0.001). Progression-free survival was also longer in the enfortumab vedotin group than in the chemotherapy group (median progression-free survival, 5.55 vs. 3.71 months; hazard ratio for progression or death, 0.62; 95% CI, 0.51 to 0.75; P<0.001). The incidence of treatment-related adverse events was similar in the two groups (93.9% in the enfortumab vedotin group and 91.8% in the chemotherapy group); the incidence of events of grade 3 or higher was also similar in the two groups (51.4% and 49.8%, respectively). Conclusions Enfortumab vedotin significantly prolonged survival as compared with standard chemotherapy in patients with locally advanced or metastatic urothelial carcinoma who had previously received platinum-based treatment and a PD-1 or PD-L1 inhibitor.