We report a case of Mediterranean lymphoma treated with antibiotics. A 74-year-old woman visited the hospital due to abdominal pain. Endoscopic examination showed erosions and ulcerations on duodenal mucosa. Biopsy specimens histologically revealed massive infiltration of small-sized lymphocytes and plasma cells in subepithelial mucosa. Immunoperoxidase staining showed that the infiltrating cells were positively stained with anti-alpha heavy chain. Serum IgA concentration was elevated and immunoelectrophoresis of the serum demonstrated monoclonal protein composed of alpha heavy chain. During the antibiotic treatment her symptoms disappeared and serum IgA concentration was normalized. Endoscopic examination also showed healing of the duodenal ulceration. The similarities between Mediterranean lymphoma and gastric mucosa-associated lymphoid tissue (MALT) type lymphoma, both of which may be related to bacterial infection and can be treated with antibiotics, are discussed in this report.