Background: The prognosis in patients with metastatic SCUC (mSCUC) remains poor with median survival around 1 year with systemic chemotherapy. We aimed to investigate the impact of ICI on survival of patients with mSCUC. Methods: Patients who received systemic therapy at MD Anderson Cancer Center (MDACC) for de novo or metachronous mSCUC after completing local management. within 12 months of neoadjuvant or adjuvant chemotherapy were included in this cohort, with overall survival (OS) calculated from the time of receipt of initial chemotherapy. Hazard ratios (HR) and 95% confidence intervals (95% CI) were calculated using logrank test. Results: 102 patients with mSCUC received systemic therapy at MDACC between April 2006 and June 2020. Median age was 66 (range 24 – 86 years), male to female ratio was 5. Bladder was the primary site in 85 (83%), 45 (44%) had prior cystectomy and 9 (9%) had prior nephroureterectomy. Histologies included 51 (50%) with predominant small cell (SC) features, 28 (27%) with focal SC features, 20 (20%) with pure SC, and 3 (3%) mixed with large cell component. Thirty-nine (38%) received ICI during their disease course: 29 (28%) following front-line chemotherapy (15 of whom within 12 months of neoadjuvant/adjuvant platinum therapy), 5 (5%) combined with front-line chemotherapy, and 5 (5%) received ICI front-line (two of whom were able to receive second-line chemotherapy). ICI agents used included anti-PD-1 (n=19), anti-PD-L1 (n=12), anti-PD-1/anti-CTLA-4 (n=5), anti-PD-1/anti-TIM3 (n=1), anti-PD-1/anti-STAT3 (n=1), anti-PD-L1/PARPi (n=1). Those who received ICI at any time had an improved median OS compared to those treated with chemotherapy alone (20.1 vs 12 months), [HR=0.45, 95% CI 0.27-0.72, p=0.003]. When we limited the analysis to those with de novo mSCUC (n=36), those who received ICI at any time (n=13) had an improved median OS compared to those treated with chemotherapy alone (n=23) (not reached vs 9.41 months), [HR=0.28, 95% CI 0.12-0.68, p=0.03]. Among patients who received ICI (n=39), median OS in those with liver metastases (n=11) was numerically shorter than those without (n=28) (13.1 vs 21.6 months), [HR=1.83, 0.59-5.7, p=0.21]. Conclusions: ICI improves OS for patients with mSCUC. Although clinical trials remain difficult in these rare variants, further prospective studies are indicated to confirm this finding.