Researchers found that overall survival (OS) in patients with advanced-stage non-small cell lung cancer (NSCLC) is improved by immune checkpoint inhibitor (ICI) monotherapy more so than by cytotoxic chemotherapy. Positive results have been seen more recently when ICI is used in conjunction with chemotherapy. Even so, ICI monotherapy was still a viable option for treatment. There was a lack of information regarding long-term progression-free survival (PFS) and OS in real-world settings. The study was conducted as a retrospective study at multiple locations. Between December 2015 and December 2018, 435 consecutive patients with a histological diagnosis of advanced, metastatic, or recurrent NSCLC who were treated with ICI monotherapy were enrolled in the study. Information regarding patient health was gathered from pharmacy and electronic medical record databases. Survival rates for these patients were 3.4 months for progression-free survival and 13.0 months for overall survival. There was a 4-year survival rate of 17.9% and rates of objective response and disease control of 22.8% and 54.9%, respectively. According to multivariate analyses, factors that were associated with a favorable progression-free survival (PFS) included patient age (>70 years), a good Eastern Cooperative Oncology Group Performance Status (ECOG PS) score, a programmed death-ligand 1 tumor proportion score [PD-L1 tumor proportion score (TPS)] of more than equal to 50%, the absence of bone metastases, and the presence of immune-related skin toxicity. In addition, a high ECOG PS score, PD-L1 TPS of more than equal to 50%, the lack of bone metastases, and the presence of skin toxicity were all associated with a long survival time. After 4 years, only 17.9% of patients survived. Positive progression-free survival (PFS) and overall survival (OS) were associated with a high ECOG performance status (PS) score, a PD-L1 tumor proportion score (TPS) of more than equal to 50%, a lack of bone metastases, and a presence of skin toxicity.