A 69-year-old woman presented with macroscopic hematuria and severe anemia. Cystoscopy revealed flat edematous mucosa with continuous bleeding. Transurethral coagulation and a biopsy of the urinary bladder were performed. Histopathological examination of the biopsy revealed non-Hodgkin's lymphoma of the mucosa-associated lymphoid tissue (MALT) type. Results of a computed tomography scan and gallium scintigraphy suggested that it was a primary malignant lymphoma of the urinary bladder. A urinary tract infection was found and she was treated with antibiotics for 2 weeks. Because of the detection of a Helicobacter pylori (HP) infection in the gastric mucosal biopsy specimens, the patient was subsequently administered HP eradication therapy. Consequently, the lymphoma disappeared and the woman has had no tumor recurrence for the past 25 months.