Background: While clinical trials have affirmed benefit of IO for mUC, limited real-world evidence exists to describe the current treatment landscape and clinical outcomes. This study evaluated these trends in a network of community oncology practices, the US Oncology Network (USON). Methods: This was a retrospective study of adult mUC pts who initiated IO regardless of PD-L1 expression in the first- (1L cohort) or second-line (2L cohort) setting between 5/1/2016-1/31/2018. Using data from USON’s electronic heath record, descriptive and Kaplan-Meier analyses were conducted to evaluate baseline characteristics, treatment patterns and clinical outcomes. Results: Among the 254 pts in the 1L cohort, median (range) age at IO initiation was 74 (42, 90+), 71% were male, 77% were Caucasian, and 18.1% and 5.9% had ECOG performance status (PS) 2 and 3/4, respectively. Among the 179 pts in the 2L cohort, median (range) age at IO initiation was 71 (29, 90+), 76% were male, 76% were Caucasian and 20.7% and 2.2% had ECOG PS 2 and 3/4, respectively. Nearly all pts received IO monotherapy. Median (range) follow-up durations from IO initiation were 4.3 (0, 22; 1L cohort) and 3.6 (0, 19; 2L cohort) months (mo), during which time 39% (1L cohort) and 37% (2L cohort) of pts died. Median overall survival (95% confidence interval [CI]) was 9.9 (7.5, 15.7) mo for the 1L IO cohort and 8.3 (6.4, not reached) mo for the 2L IO cohort. Six-mo survival probabilities (95% CI) were 61.6% (54.5%, 67.9%; 1L cohort) and 60.7% (51.4%, 68.8%; 2L cohort). In total, 52.8% of 1L pts and 53.6% of 2L pts were alive and did not advance to next line of therapy, and 11% of 1L and 13% of 2L cohort pts advanced to the next line of therapy. Median (95% CI) treatment durations were 2.3 (1.9, 3.0) and 3.3 (2.7, 3.9) mos for the 1L and 2L cohorts, respectively. Six-mo ongoing treatment probabilities (95% CI) were 28.9% (23.3%, 34.7%; 1L cohort) and 34.0% (26.1%, 42.1%; 2L cohort). Conclusions: Outcomes of real-world mUC pts receiving IO were as expected, with majority of pts alive and a small minority receiving post-IO therapy. Future research should examine how pt and tumor (PD-L1 expression) characteristics influence treatment and outcomes.