In the last few years, immunotherapy has become part of everyday clinical practice for the treatment of many solid tumors including metastatic non-small-cell lung cancer. These drugs, however, can yield a specific toxicity profile that consists of immune-related adverse events (irAEs). Hepatotoxicity is one of irAEs and occurs in about 1-3% of cases and may be manifested by the presence of increate levels of liver enzymes (aspartate aminotransferase, alanine aminotransferase) and/or biliary stasis evidence; in these cases, a differential diagnosis with other hepatic diseases must be considered. We present the case of a 73-year-old man who presented with an alteration in liver function during treatment with pembrolizumab (anti-programmed death 1 monoclonal antibody) for a stage IV nonsquamous non-small-cell lung cancer, which was initially mistaken for drug-induced irAEs hepatic toxicity.