Genetic mutations that render mismatch repair defective may result in microsatellite instability, which is common in colorectal carcinomas and gastric cancers as well as Lynch syndrome. Mismatch repair deficiency/high microsatellite instability (dMMR/MSI-H) predicts the tumor response to immune checkpoint inhibitors. However, few studies have evaluated the efficacy of immune checkpoint inhibitors in non-small cell lung cancer (NSCLC) patients with dMMR/MSI-H. In this work, we present a patient with advanced squamous lung cancer with dMMR/MSI-H and a high tumor mutational burden (TMB-H) who obtained a long-term benefit from immunotherapy. NSCLC patients with dMMR/MSI-H/TMB-H may thus benefit from immune checkpoint inhibitors.