We report the case of a 73-year-old man who presented with a 2- to 3-month history of epigastric discomfort and guaiac-positive stool. An upper gastrointestinal endoscopy revealed a diffuse erythematous nodular mucosa and submucosal thickening in the stomach. Diffuse mucosal nodularity was also found in the second portion of the duodenum. A complete workup with histologic, immunohistochemical, and molecular studies revealed 2 distinct, apparently unrelated lymphomas, namely, a gastric marginal zone B-cell lymphoma (mucosa-associated lymphoid tissue type) in a background of Helicobacter pylori gastritis and a grade 1/3 duodenal follicular lymphoma. The patient was then treated with an H pylori eradication regimen. No therapy was given for his duodenal follicular lymphoma because his symptoms were thought to be due to the gastric disease and because the duodenal lesion was small. A 6-month follow-up with upper gastrointestinal endoscopy revealed only focal biopsy scarring in the stomach and an apparently normal duodenum. The follow-up biopsies revealed significant regression of his mucosa-associated lymphoid tissue lymphoma, but persistence of his duodenal follicular lymphoma. The combination of these 2 lymphomas in the same patient and the different clinical responses to antibiotic treatment make this case unique.