A 64-year-old woman visited our hospital in December 2005 because of general malaise. Her hemoglobin level was 9.0 g/dl. Gastrointestinal fiberscopy detected a hemorrhagic gastric ulcer, which was considered as etiology of anemia. Abdominal ultrasonography showed bilateral hydronephroses and hydroureters. A urine test revealed pyuria and macroscopic hematuria, and urine culture revealed 10(8) colony-forming units of Escherichia coli per ml. Pelvic MRI showed thickening of the posterior wall and trigone of the urinary bladder. Transurethral resection was peformed, and biopsy of the mucous of the bladder gave a diagnosis of primary mucosa-associated lymphoid tissue (MALT) lymphoma of the urinary bladder. Ann Arbor clinical stage was IEA. It was planned to administer irradiation at a total dose of 36 Gy to the whole bladder and part of the tumor; however, radiotherapy was discontinued at a dose of 26 Gy because of the development of pollakisuria. Pelvic MRI and pathologic examination of the urinary bladder after radiotherapy showed that the lymphoma was in complete remission; however, she received retuximab therapy at a dose of 375 mg/m2/week, 8 times additionally, because of the reduced radiotherapy. The patient has remained in complete remission for 14 months.