The development of simultaneous primary gastric lymphoma and carcinoma is a rare event for which a possible etiopathogenetic role for Helicobacter pylori (HP) recently has been postulated. We report a series of eight such cases diagnosed from 1980 to 1995. In two cases, both tumors arose in a gastric stump, at 26 and 34 years, respectively, after gastric resection for a duodenal ulcer. Grossly, the lymphoma and carcinoma formed a single lesion in four cases (collision tumor); they were separated in the other four cases. Histologically, all the lymphomas fit into the category of B-cell mucosa-associated lymphoid tissue lymphoma; six of them were low-grade lymphomas and two were low-grade lymphomas with a high-grade component. The adenocarcinomas were intestinal-type in four cases, diffuse in three, and mixed in one. Regarding the depth of infiltration, four carcinomas were early gastric cancers and four were advanced. All the collision tumors contained an early gastric cancer. Our observations confirmed the association of HP with gastric lymphoma and carcinoma in 4 cases. Spiral bacteria with the features of Helicobacter heilmannii were found in one case. The occurrence of two different tumors in a gastric stump, which has not been reported previously, suggests that postgastrectomy gastritis might contribute to the development of both gastric lymphoma and carcinoma.