AbstractPurposeImmune‐checkpoint inhibitors (ICIs) are effective against advanced non‐small cell lung cancer (NSCLC). However, whether the efficacy and safety of ICI treatment in elderly patients are similar to those in younger patients is unclear. This study was designed to address this question.MethodsWe enrolled patients who received ICI monotherapy in Japan between December 2015 and December 2017; those ≥75 years of age comprised the elderly group. We compared the efficacy and safety of ICI monotherapy in elderly patients with those in younger patients and explored prognostic factors in elderly patients.ResultsWe enrolled 676 patients; 137 (20.3%) were assigned to the elderly group. The median age of the elderly and younger groups was 78 (range, 75–85) and 66 (range, 34–74) years. The median progression‐free survival (4.8 months vs. 3.3 months,p= 0.1589) and median overall survival (12.3 months vs. 13.0 months,p= 0.5587) were similar between the elderly and younger groups. Multivariate analysis revealed that a significantly better OS in the elderly group was associated with better responses to first‐ or second‐line ICI treatment (p= 0.011) and more immune‐related adverse events (irAEs) (p= 0.02). IrAEs that led to ICI discontinuation occurred in 34 of 137 patients (24.8%) in the elderly group, and their survival was significantly higher than that in those who did not have irAEs.ConclusionICI is also effective in elderly NSCLC patients, and treatment discontinuation due to irAEs may be a good prognostic marker.