Langerhans cell histiocytosis (LCH) of the alimentary tract is a rare condition, and LCH of the stomach especially so. We report a histologically and endoscopically unusual case of gastric LCH, the diagnosis of which was based on gastric mucosal biopsy specimens from an adolescent with multi-organ LCH and striking gastric polyposis. Microscopically, the gastric mucosa was expanded by discrete granulomatous microaggregates of Langerhans cells, resulting in a close resemblance to other, more common nonnecrotizing granulomatous gastritides. The diagnosis of LCH was confirmed immunohistochemically and ultrastructurally. To our knowledge, this is the first report of gastric LCH with a granulomatous histologic pattern, and the third to cause diffuse gastric polyposis. Langerhans cell histiocytosis should be included in the histologic differential diagnosis of granulomatous gastritis, as well as in the endoscopic differential diagnosis of gastric polyposis.