Primary plasmacytoma of the gastrointestinal tract is a rare entity. We report a case of a primary gastric plasmacytoma in a 57-year-old man who presented with upper-gastrointestinal bleeding. Endoscopy showed a nodular gastric mass with central umblication. Histological examination of the gastrectomy specimen revealed a monoclonal lambda-chain extramedullary plasmacytoma. Further staging was found to be negative for multiple myeloma. As other more common pathologic processes at this site may also be endowed with numerous plasma cells, awareness of this entity and distinction using immunohistochemistry are extremely crucial. Because systemic disease ultimately develops in many patients with localized plasmacytoma, such patients should be followed closely for the appearance of clinical, biochemical, and roentgenologic evidence of multiple myeloma.