BACKGROUND Few articles have analyzed the prognostic data from a large series of primary gastric lymphoma classified according to the concept of mucosa-associated lymphoid tissue (MALT). METHODS The resected specimens from 233 patients with primary gastric lymphoma were investigated retrospectively, including immunostaining with MIB-1 (Ki-67). RESULTS Histologically, 70 (30%) of the cases were low grade B-cell lymphoma of MALT, 27 (12%) low grade B-cell lymphoma of MALT with a focal high grade component, 100 (43%) high grade B-cell lymphoma of MALT, 15 (6%) other B-cell lymphomas, 14 (6%) T-cell lymphomas, and 7 (3%) undetermined. Macroscopically, 96 (41%) were superficial-spreading type, 100 (43%) mass-forming, 14 (6%) diffuse-infiltrating, and 23 (10%) unclassified. The MIB-1 index correlated with phenotype, histologic grade, stage, depth of invasion, and macroscopic type. A significantly better survival was noted for young patients, and those with tumors of a B-cell phenotype, histologic low grade, macroscopic superficial-spreading type, low stage, low depth of invasion, and low MIB-1 index. No significantly different survival rates were found between the patients who underwent gastric resection alone and those who also received additional chemotherapy. By Cox multivariate analysis, independent prognosticators included B-cell phenotype, low stage, and macroscopic superficial-spreading type. CONCLUSIONS In addition to stage, phenotype and macroscopic type are also important prognostic indicators of primary gastric lymphoma. Immunostaining with MIB-1 had limited independent value for predicting prognosis.