Behçet's disease is chronic, relapsing, multi-systemic inflammatory vasculitis. Unlikely the other autoimmune diseases, gastric non-Hodgkin's lymphoma has rarely been reported in a patient with Behçet's disease. We report here on a 40-year-old man who had Behçet's disease for several years and who suffered recurrent oral ulcer, genital ulcer and skin lesion. The patient was treated with azathioprine and intermittent oral steroid. He complained of epigastric pain for 1 month, and he had a large ulcerative lesion seen on endoscopic evaluation. We confirmed the lesion was a gastric, diffuse, large B cell lymphoma by endoscopic biopsy. The patient was treated with the rituximab-CHOP regimen, and he has achieved a complete remission for 3 years. We report here on a case of gastric non-Hodgkin's lymphoma in a patient with Behçet's disease and who also had an ileocecal valve ulcer. (Korean J Gastrointest Endosc 2010;40:252-255)