BACKGROUND: Primary gastric non-Hodgkin's lymphoma (PG-NHL) is common in Saudi Arabia. This has prompted the analysis of a large series of patients with PG-NHL having high-grade diffuse large B-cell lymphoma (DLCL) in order to define the clinical features and outcome of this disease. PATIENTS AND METHODS: The data of all adult patients in the series with PG-NHL having DLCL histology were retrospectively reviewed. Patients were eligible if they had biopsy-confirmed diagnoses obtained by endoscopy or following laparotomy. RESULTS: Over a 16-year period, 185 patients with DLCL PG-NHL were identified and their data were reviewed. Patients had a median age of 54 years. In 53% of them only one initial therapeutic modality was given, while 47% were managed by a multi-modality approach. One hundred forty patients (76%), 19 (10%), and 26 (14%) attained complete remission (CR), partial remission, and no response/progressive disease, respectively. Multivariate analysis showed that poor performance status and advanced stage were negatively associated with the likelihood of attaining CR. Over a median follow-up of 54 months, 118 (64%) of the patients were alive and disease-free, 17 (9%) were alive with evidence of disease, and the remaining 50 (27%) were dead. The projected 5-year and 10-year overall survivals (OS) (+/- SD) were 68% (+/- 4%) and 61% (+/- 6%), respectively. The Cox proportional hazards model identified the same variables of response as adverse prognostic factors of survival. Using the influence of performance status, and stage, a prognostic index was constructed to recognize three prognostically distinctive risk categories with overall survival proportions of 87%, 61%, and 45%, respectively. The unadjusted International Prognostic Index, however, failed to classify patients into prognostically meaningful risk strata. Of the 140 patients who achieved CR, the median disease-free survival (DFS) was not reached, but the predicted 5- and 10-year DFS were 82% and 75%, respectively. A multivariate analysis identified poor performance status as the only independent prognostic covariate that adversely influenced DFS. Our analysis showed that compared with single-modality management, multi-modality strategy attained significantly higher CR, and advantageous OS and DFS. CONCLUSIONS: This large series characterized the clinico-pathologic features and outcome of patients with DLCL PG-NHL. Performance status, and stage significantly influenced patient outcome. A prognostic index was developed and it identified three prognostically distinctive risk groups; however, prospective validation is warranted.