A 78-year-old woman was admitted to our department because of the incidental finding during routine abdominal ultrasound examination of a large aneurysm of the superior mesenteric artery. Presence of the aneurysm was confirmed at computed tomography and digital subtraction angiography, but its inflammatory origin was not recognized. No other aneurysm localization was found. Macroscopic intraoperative findings suggested the inflammatory nature of the lesion, but only histopathologic examination was diagnostic. Aneurismorraphy with prosthetic in-line reconstruction was performed. This report presents the previously undescribed possibility of an isolated inflammatory aneurysm of the superior mesenteric artery.