Primary small intestinal lymphoma (PSIL) is often treated with surgical resection, and therefore response to non-surgical treatment is rarely known. We retrospectively analyzed the clinicopathological features of 19 patients with PSIL, who had been diagnosed by double-balloon endoscopy (DBE) and had not received surgical treatment. The immunohistological phenotypes of 18 patients were B-cell lymphomas. Five patients had tumors within the jejunum, nine within the ileum and five in multiple sites including the duodenum. Most cases were in the low or low-intermediate risk group of the International Prognostic Index score. Seventeen patients received chemotherapy, with an overall response rate of 82.4%. The estimated overall survival at 5 years was 72.2%. Response to initial chemotherapy and levels of hemoglobin (Hb) and albumin (Alb) were identified as favorable prognostic indicators. We conclude that PSIL can be effectively diagnosed by DBE and shows a good prognosis with chemotherapy alone.