Background: Data from interim analysis of IMvigor130 trial showed that 1st line treatment of advanced urothelial cancer (aUC) with atezolizumab (Atezo) + platinum-based chemotherapy (PBC) significantly improved progression-free survival (PFS), but not overall survival (OS), vs PBC. Switch maintenance anti-PD(L)1 after completion of PBC as 1st line therapy is an alternate strategy, recently reported to significantly prolong OS. We aimed to compare cost-effectiveness of combined treatment (Atezo+PBC) vs PBC based on IMvigor130. Methods: We used a partitioned-survival model to evaluate the potential cost-effectiveness of treatment with A) Atezo+PBC (gemcitabine with cisplatin or carboplatin) or B) PBC alone with checkpoint inhibitor pembrolizumab at progression (standard-of-care). PFS and OS curves were extracted from IMvigor 130 and parametric models were fit to approximate outcomes with Atezo+PBC with the hazard ratio (HR) from the trial used to project outcomes for PBC alone. We used a health-care payer perspective with a two-year time horizon. Model outputs — costs, life-years, quality-adjusted life years (QALYs) — were used to calculate an incremental cost-effectiveness ratio (ICER). A scenario analysis evaluated the “value-based price” needed for Atezo+PBC to be cost-effective; a one-way sensitivity analysis was also performed. Results: Results of the cost-effectiveness analysis are summarized in the table. The mean projected incremental cost of Atezo+PBC compared to PBC was $59,604 for a mean incremental gain of 0.09 life-years and 0.07 QALYs. This resulted in an ICER of $629,755/life-year and $895,800/QALY, respectively. A 33% reduction would be needed in the price of atezolizumab to make Atezo+PBC cost-effective at an ICER of $150,000/QALY. Results were sensitive to cost of pembrolizumab at progression, the cost of Atezo+PBC, and the OS HR between Atezo+PBC and PBC. Conclusions: Combined chemoimmunotherapy with atezolizumab and PBC would likely not be cost-effective for the first-line treatment of aUC. However, with a price rebate of 33%, it would approach being cost-effective at a widely used cost-effectiveness threshold.