An 84-year-old man consulted a local physician for asymptomatic macrohematuria. Abdominal ultrasonography revealed thickening ofthe bladder wall from the triangular part ofthe bladder to the posterior wall, and he was referred to our department. Cystoscopy showed extensive bladder wall thickening with edema ofthe mucosa. Abdominal contrast-enhanced computed tomography (CT) showed extensive bladder wall thickening and right external iliac lymphadenopathy accompanied by a contrast effect suspected ofbeing extravesical invasion. We performed transurethral resection ofthe bladder tumor and made the diagnosis ofmucosa associated lymphoid tissue (MALT) lymphoma. Our diagnosis made from positron emission tomography-CT performed after surgery was primary MALT lymphoma of the bladder and metastasis to the right external iliac lymph node. We administered rituximab 375 mg/m2 once a week for four times in total. CT after rituximab administration showed that the tumor and right external iliac lymph nodes had shrunk significantly, and no recurrence was present at 18 months after treatment.