BACKGROUND: Cisplatin-based chemotherapy remains the mainstay treatment for advanced lung cancer; however, it remains controversial whether the efficacy of chemotherapy can be modulated by the immune-checkpoint status. In this study, we investigated the relationship between programmed cell death-ligand 1 (PD-L1) expression status and the efficacy of cisplatin-based chemotherapy by using individual patient data and pathological specimens obtained during our two previously performed prospective studies on the feasibility of short-term low-volume hydration in patients with advanced lung cancer who received cisplatin-based chemotherapy. METHODS: Among 91 patients who participated in the two aforementioned trials, those with assessable tumor specimens were included in this sub-analysis. PD-L1 expression levels were determined using immunohistochemical staining, while the Response Evaluation Criteria in Solid Tumors, version 1.1, were used for determining treatment efficacy. RESULTS: Thirty-two patients were investigated. PD-L1 expression was observed in 8 patients (25.0%; the PD-L1-positive group), with 2 exhibiting a PD-L1 expression of 50% or more. None of the patients in the PD-L1-positive group responded to treatment, while the overall response rate in the PD-L1-negative group was 20.8% (5 of 24; P = 0.296). Both the progression-free survival and overall survival rates were worse in the PD-L1-positive group than in the PD-L1-negative group (3.7 vs. 5.9 months [P = 0.018] and 5.8 vs. 37.3 months [P = 0.070], respectively). CONCLUSION: PD-L1 expression was negatively correlated with survival in patients receiving cisplatin-based chemotherapy.