We report herein the case of a 57-year-old man in whom malignant lymphoma originating in the gastric remnant was confirmed 25 years after a subtotal gastrectomy with Billroth II reconstruction had been performed for gastric ptosis. Gastroscopy revealed an ulcerated tumor on the fornix, and histologic examination of the endoscopic biopsy specimens demonstrated malignant lymphoma. Thus, total gastrectomy with splenectomy, pancreatectomy, and resection of the previously anastomosed jejunal stoma were performed. Histologic examination of the stomach remnant confirmed a diagnosis of B-cell lymphoma of the large-cell type. Although we were unable to study the surgical specimen from the initial operation, the possible relationship between pseudolymphoma and malignant lymphoma has been presented in the literature, which is reviewed following this case report.