A 28-year-old white man presented to the gastrointestinal (GI) medicine clinic for persistent nausea and vomiting. He had a long-standing history of gastroesophageal reflux disease that was only partially controlled with proton pump inhibitor therapy. The symptoms were exacerbated by cessation of proton pump inhibitor medication, and he reported an associated 9-kg weight loss. Results of laboratory testing were significant for iron deficiency anemia (hematocrit, 31% [to convert to proportion of 1.0, multiply by 0.01]) and hemeoccult-positive stool. Upper and lower endoscopy, computed tomography enterography, PillCam capsule endoscopy, and a Meckel scan failed to identify a source of GI bleeding. The patient received a retrograde double-balloon enteroscopy that showed an outpouching in the distal ileum (Figure, A) with an accompanying ulceration of the adjacent mucosa (Figure, B). Exploratory laparotomy with small-bowel resection was performed, and the gross specimen is shown in Figure, C.