Summary Yttrium-90 microsphere radioembolization (90Y MRE) is a therapy for liver malignancies by permanently implanting 90Y-containing microspheres into tumors via hepatic artery. The etiology of persistent gastric ulcerations in patients presenting months after treatment remains unclear. Three patients who presented with gastric ulceration 4 to 13 months after 90Y MRE were examined by esophagogastroduodenoscopy and biopsies. Pathological examinations showed multiple 90Y microspheres scattered within the lamina propria and submucosa. Most of the microspheres were distributed in a linear fashion, consistent with an intravascular location; however, the vascular lumen and endothelial cells were not present. The microspheres were surrounded by fibrotic tissue infiltrated by chronic inflammatory cells and rare neutrophils. Epithelial granulation without pititis and miniaturized glands with intervening fibrosis were noted, compatible with chronic ischemic changes. These findings suggest that the persistent gastric ulceration is a result of localized ischemic injury in response to 90Y MRE-induced vascular damage.