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BACKGROUND A recent study demonstrated that immune-checkpoint molecules are associated with tumoral immune evasion. MATERIALS AND METHODS Programmed cell death protein 1 (PD-1) expression on CD4+ and CD8+ T-cells obtained from gastric cancer tissue was evaluated by multicolor flow cytometry. Immunohistochemical staining was also performed to evaluate programmed cell death ligand-1 (PD-L1) expression on gastric cancer cells. RESULTS There were statistically significant correlations between PD-L1 expression and age, histology, tumor size, depth of invasion, lymph node metastasis, lymphatic vessel invasion, venous invasion, and disease stage. The 5-year survival rates of patients with and without PD-L1-positive tumors were 48.9% and 80.7%, respectively, and the difference was statistically significant. Multivariate analysis indicated that PD-L1 expression was an independent prognostic indicator. The frequency of PD-1-positive CD4+ and CD8+ T-cells from gastric cancer tissue with PD-L1 expression was significantly more than that from gastric cancer tissue without PD-L1 expression. CONCLUSION PD-L1 expression was related to a poor prognosis in patients with gastric cancer. Furthermore, PD-1 expression on T-cells was up-regulated in patients with tumors with PD-L1 expression.