Ulcerative colitis has been recognized as a premalignant condition because a considerable proportion of patients with colitis eventually develop colorectal carcinoma at the site of the inflammatory disease. Malignant lymphoma occurring in cases of long-standing ulcerative colitis is rare. Cancer risk is positively correlated with duration and anatomic extent of colitis, but do not appear to be increased by early age at onset of disease. Patients with chronic ulcerative colitis should have periodic rectal and colonoscopic biopsies, and those with moderate to marked dysplasia require colectomy because of the increased risk of colon carcinoma. We report a case of malignant lymphoma in patient with ulcerative colitis. (Korean J Gastrointest Endosc 2001;23:188-191)