Background: Recent studies indicate that PD-1 and PD-L1 checkpoint inhibitors have activity in chemotherapy refractory patients with muscle invasive (MIBC) and metastatic (mBCa) bladder cancer. PD-L1 expression on tumor cells or lymphocytes may correlate with response to therapy. To identify potential patients who may benefit from PD-1/PD-L1 targeted immunotherapeutics, we utilized a non-invasive blood test to evaluate PD-L1 protein expression in CTCs and WBCs of bladder cancer patients. Methods: Blood samples from 22 patients with MIBC or mBCa were collected at UCSF and shipped to Epic Sciences. All nucleated cells were subjected to immunofluorescent (IF) staining and CTC identification by fluorescent scanners and algorithmic analysis. Cytokeratin (CK+) expressing CTCs (CK+, CD45-, intact nuclei morphologically distinct from WBCs) as well as CK- CTCs were enumerated and correlated with available clinical data. A subset of patient samples underwent further genetic characterization by FISH. Results: CTCs were detected in 19/22 (86.4%) patients, inclusive of CK(+) CTCs (12/22, 55%), CK(-) CTCs (14/22, 70%), CK(+) CTC Clusters (6/22, 27%), and apoptotic CTCs (12/22, 54%). Seven of 22 (32%) patients had PD-L1(+) CTCs; 4 of these patients had exclusively CK(-)/CD45(-)/PD-L1(+) CTCs. A subset of CTCs were secondarily confirmed as bladder cancer via FISH. High PD-L1(+)/CD45(-) CTC burden was associated with poorer overall survival (HR: 3.29, log-rank p = 0.041) Conclusions: Patients with MIBC and mBCa who have detectable PD-L1(+) CTCs, and patients with high PD-L1(+) CTCs have worse survival compared to patients with low or absent PD-L1 expression.