Background: The programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway inhibits the activation of T cells and plays a crucial role in the negative regulation of cellular and humoral immune responses. Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoid malignancy in adults. In the present study, we aimed to detect the expression of PD-L1 in DLBCL and to analyze its relationship with prognosis. Methods: We reviewed medical records of 204 newly diagnosed DLBCL patients in Sun Yat-sen University Cancer Center between October 2005 and August 2012. The expression of PD-L1 in tumor tissues from these 204 patients was detected using immunohistochemical (IHC) assay. The expression of anaplastic lymphoma kinase (ALK), CD5, CD30, and C-Myc in tumor specimens from 109 patients was detected using IHC, and Epstein-Barr virus (EBV)encoded RNAs (EBERs) were detected using fluorescence in situ hybridization. The Spearman method was used for correlation analysis. The Kaplan-Meier method with log-rank test was used for univariate analysis. Cox proportional hazards model was used for multivariate analysis. Results: Of the 204 patients, 100 (49.0%) were PD-L1-positive in tumor cells and 44 (21.6%) were PD-L1-positive in tumor microenvironment. PD-L1 expression in tumor cells and tumor microenvironment were more common in the non-germinal center B-cell-like (GCB) subtype than in the GCB subtype (P = 0.02 and P = 0.04). Patients with PD-L1 expression in tumor microenvironment were more likely to be resistant to first-line chemotherapy when compared with the patients without PD-L1 expression in tumor microenvironment (P = 0.03). PD-L1 expression in tumor microenvironment was negatively correlated with C-Myc expression (r = -0.20, P = 0.04). No correlations were detected between PD-L1 expression and the expression of ALK, CD5, and CD30 as well as EBERs. The 5-year overall survival (OS) rates were 50.0% and 67.3% in patients with and without PD-L1 expression in tumor cells (P = 0.02). PD-L1 expression in tumor cells was an independent risk predictor for OS (P < 0.01). Conclusions: PD-L1 expression is more common in the non-GCB subtype than in the GCB subtype. PD-L1 expression in tumor microenvironment has a negative correlation with C-Myc. PD-L1 positivity predicts short survival in DLBCL patients. For patients with PD-L1 expression, more strategy such as anti-PD-L1 antibody treatment should be recommended.