Immune checkpoint inhibitors are widely used for treatment of many advanced malignancies. Lower gastrointestinal (GI) side effects, such as diarrhea and colitis, are common, but upper GI side effects are rarely reported. Consequently, the correct treatment of upper GI adverse events has been less frequently described.We describe a case of a 16-year-old woman with stage IIIb malignant melanoma treated with adjuvant monotherapy using Nivolumab. The patient developed severe gastritis after six series of Nivolumab with weight loss, nausea, and vomiting. There was no effect of intravenous steroids, but the patient´s condition resolved after administration of Infliximab.This case report supports the same treatment for gastritis as for colitis, which is in line with current guidelines.