BACKGROUND CRS (cytokine release syndrome) is a massive activation of the inflammatory system characterized by a supra-physiological rate of inflammatory cytokines. The interleukin 6 cytokine plays a central role in CRS. The main clinical sign of CRS is fever, but CRS can lead to multiple organ failure in severe cases. CRS is usually described in sepsis, more recently in SARS COV-2 infection, and in chimeric antigen receptor T-cell therapy. However, it can also be associated with immune checkpoint inhibitors (ICIs), which is infrequently described. ICI have growing indications and can lead to CRS by causing an uncontrolled activation of the immune system. There are currently no treatment guidelines for ICI-induced CRS. CASE REPORT We report a rare case of grade 3 CRS induced by nivolumab associated with 5-fluorouracil and oxaliplatin for gastric cancer. The patient was 65-year-old man with an adenocarcinoma of the cardia. CRS developed during the tenth course of treatment and was characterized by fever, hypotension requiring vasopressors, hypoxemia, acute kidney injury, and thrombopenia. The patient was transferred quickly to the Intensive Care Unit. He was treated for suspected sepsis, but it was ruled out after multiple laboratory examinations. There was rapid resolution after infusion of hydrocortisone. CONCLUSIONS The use of ICIs is expanding. Nivolumab-induced CRS is rarely described but can be severe and lead to multiple organ dysfunction; therefore, intensive care practitioners should be informed about this adverse effect. More studies are needed to better understand this condition and establish treatment guidelines.