There is growing interest for biomarkers that allow a better selection of non-small cell lung cancer (NSCLC) patients that are likely to benefit from immunotherapy. To date, several biomarkers are under investigation, including the PD1/PL-L1 axis, the tumour mutational burden, and the gut microbiota. The gut microbiota seems interesting due to its role in cancer, cancer treatment and treatment-related toxicities. Below we briefly summarize the conditions that might influence the composition of the gut microbiota and the subsequent effect on a response to immunotherapy, immune-related adverse events, and their management in NSCLC.1