ABSTRACTImmune checkpoint inhibitors have revolutionized oncologic treatment. However, they are linked to various side effects,1a rare one being gastrointestinal eosinophilia. We present a patient with malignant melanoma treated with nivolumab. She underwent upper endoscopy 6 months later which showed a duodenal ulcer and linear furrows of her esophagus. Biopsies of the esophagus, stomach, and duodenum were consistent with eosinophilic infiltration. Repeat endoscopy after nivolumab discontinuation revealed near-complete resolution of eosinophilia in the stomach and duodenum, with lingering eosinophilia in the esophagus. The purpose of this report was to increase awareness of gastrointestinal eosinophilia associated with checkpoint inhibitors.