Primary gastrointestinal lymphoma is a rare disease, and a primary rectal diffuse large B cell lymphoma is rarely encountered. We report a case of a 60-year-old woman with diffuse large B cell lymphoma in the rectum. The patient underwent a low anterior resection six years ago due to a sigmoid colonic adenocarcinoma. The patient had multiple polypoid lesions on the rectum, and the patient was diagnosed with primary rectal diffuse large B cell lymphoma after a biopsy. There were no other lesions detected on a chest and abdomen CT scan. After the administration of combination chemotherapy, the polypoid lesions disappeared. (Korean J Gastrointest Endosc 2008;36: 302-306)