The simultaneous occurrence of primary gastric lymphoma and adenocarcinoma is rarely reported. We here report a case of synchronous double primary tumor of advanced gastric cancer and diffuse large B cell lymphoma. A 65-year-old woman underwent an esophagogastroduodenoscopy for the evaluation of abdominal discomfort of two months` duration. The endoscopic examination showed an ulcerating tumor in the gastric antrum and thickened folds in the fundus and the microscopic examination revealed an adenocarcinoma in the antrum and a diffuse large B-cell lymphoma in the fundus. She has had total gastrectomy and CHOP chemotherapy with rituximab. Since the cases of synchronous double primary gastric tumors have been increased on the recent medical advances, when a gastric tumor is detected for the endoscopic examination, an endoscopist has to make every endeavor not to miss another tumor in the stomach. (Korean J Gastroenterol 2011;57:115-119)