Immune checkpoint inhibitors (ICI) are increasingly used to treat solid tumors. With growing use, numerous toxicities have been recognized, many of which are believed to be secondary to dysregulated autoimmune inflammatory responses. Although PD-L1 antibody toxicities in the lower gastrointestinal tract, including diarrhea and colitis, are widely described, adverse effects in the upper gastrointestinal tract are rarely reported. We describe a patient with severe esophagitis, gastritis, and duodenitis following atezolizumab treatment for urothelial cancer. A 71-year-old male with metastatic invasive papillary urothelial carcinoma was admitted to The University of Chicago Hospitals for Klebsiella urosepsis. Eight weeks prior to admission he was enrolled in a clinical trial of anti-PD-L1 antibody atezolizumab and completed two cycles of therapy. On the current admission, the patient developed dysphagia as well as odynophagia that gradually progressed to inability to tolerate even liquids.He denied abdominal pain or diarrhea. Esophagogastroduodenoscopy was performed that was notable for severe, circumferential LA Grade D esophagitis, diffuse gastritis, and severe duodenitis with multiple cratered duodenal ulcers. Biopsies obtained from the esophagus showed deep ulcerations with involvement of the underlying smooth muscle, consistent with drug-induced injury. The only other potential offending medication was an NSAID, which he used infrequently. A GMS histochemical stain and immunostains for HSV and CMV were negative. The patient was started on twice daily PPI with improvement in both dysphagia and odynophagia. Follow-up EGD, however, could not be performed as the patient subsequently expired following a cardiac arrest. Immune checkpoint inhibitors are increasingly used to treat solid tumors. It is, therefore, important to recognize their toxicities. While colitis secondary to these agents is well-described, upper GI toxicities have rarely been reported. We believe, therefore, that this case report will help serve to alert gastroenterologists and oncologists of their little reported, but potentially severe proximal gut toxicities.1906_A Figure 1. Lower third of the esophagus - diffuse esophagitis1906_B Figure 2. Erythematous, hyperemic gastric body1906_C Figure 3. Erythematous, hyperemic second portion of the duodenum with duodenal ulcer