394 Background: Cisplatin-based chemotherapy is currently the standard 1L treatment for mUC, but many pts are ineligible and progression is common. Atezo (anti–PD-L1) is approved for certain types of mUC, and long-term efficacy and safety have been shown (Balar, ASCO 2018). Elderly pts in particular tend to have poor outcomes and may be chemotherapy intolerant, so this analysis sought to evaluate clinical outcomes in pts aged ≥ 65 and ≥ 75 y from the Phase II IMvigor210 study. Methods: This 2-cohort, single-arm study enrolled pts ineligible for 1L cisplatin and previously platinum-treated pts. Atezo 1200 mg IV q3w was given until PD (Cohort 1) or loss of clinical benefit (Cohort 2). RECIST v1.1 ORR (independent review; primary endpoint) and DOR and OS (secondary) were evaluated in pt subgroups based on PD-L1 status and age. Results: Evaluable pts as of July 12, 2018, are shown in the Table. In Cohort 1 pts ≥ 75 y, ORR was 29% overall, CR rate was 8%, DOR was NE and median OS was 21.4 mo. In Cohort 2 pts ≥ 75 y, ORR was 23%, CR rate was 7%, mDOR was 20.9 mo and mOS was 9.2 mo. Updated safety analyses in elderly pts will be presented. Conclusions: Efficacy outcomes in IMvigor210 elderly pts with mUC, and PD-L1 subgroup analysis appear generally consistent with those in the overall population in this long-term analysis. (Cohort 1; Balar Lancet 2017; NCT02951767). (Cohort 2; Rosenberg Lancet 2016; NCT02108652). Clinical trial information: NCT02951767 and NCT02108652. [Table: see text]