Background: Immune checkpoint inhibitor (ICI) has become the standard therapy for metastatic non-small cell lung cancer (NSCLC) patients. However, no robust evidence on the efficacy and safety of ICI in elderly NSCLC patients has been established. Materials and Methods: This retrospective study aimed to assess the efficacy and safety of ICI in elderly NSCLC patients. NSCLC patients treated with ICI monotherapy or chemoimmunotherapy (CIT) between 2016 and 2022 were divided into two cohorts according to the age: the Elderly cohort (patients aged ≥ 75 years) and the Nonelderly cohort (patients aged