Abstract Purpose PD-1 ligand (PD-L1) is expressed on both tumor cells (TCs) and tumor immune cell infiltrates (TIMC). In metastatic bladder cancer, increased TIMC PD-L1 positivity (PD-L1+) was correlated with better overall survival, however, in high grade T1 bladder tumors (HGT1) PD-L1+ on TCs and TIMCs, and correlation with outcome or pathological features remain unknown. Materials and Methods Formalin-fixed paraffin embedded (FFPE) tumor samples from 140 clinically annotated HGT1patients (pts) were retrieved. All pts were initially diagnosed with HGT1 by transurethral resection (TUR), subsequently received BCG, and had a median follow up of 7.4 years. PD-L1+ on the initial TUR was evaluated by immunohistochemistry using a mouse monoclonal anti-PD-L1 antibody (405.9A11). TC PD-L1+ was defined as 5% of TC membrane staining. TIMC PD-L1+ was scored on the extent of infiltrate and percentage of positive cells. Fisher's exact test assessed the associations of PD-L1+ with disease outcomes, carcinoma in situ (CIS) presence, and difference between HGT1 and MIBC. Results Among 140 HGT1 pts, TCs and TIMC PD-L1+ was seen in 6 (4%) pts and 48 (34.3%) pts, respectively. In a subset of 106 patients with adequate follow up, PD-L1+ was not correlated with disease outcomes on TCs (p=0.3) nor TIMC (p=0.47). PD-L1+ did not correlate with the presence of CIS. TC PD-L1+ was significantly less in HGT1 compared to MIBC(p<0.001). Conclusions PD-L1 is widely expressed on TIMCs, but not on TCs in HGT1. We did not find a correlation between PD-L1+ and outcome or CIS presence. TC PD-L1+ is significantly lower in HGT1 compared to MIBC.