Involvement of the lower urinary tract by advanced non-Hodgkin's lymphoma (NHL) has been reported in up to 13% of cases, but primary NHL of the urinary bladder is very rare. A 35-year-old man was admitted to our hospital with a chief complaint of gross hematuria with left flank pain on April 12, 2001. Cystoscopy revealed an edematous broad-based mass on the left lateral wall of the bladder, and transurethral biopsy showed NHL, diffuse large B-cell type. Abdomino-pelvic CT scan demonstrated left-side hydronephrosis and hydroureter with left proximal ureter infiltration and thickening of the left lateral wall of the bladder with perivesical fat infiltration without lymph node enlargement. Full-scale staging work-up revealed the bone marrow as the solely involved site. The lesions of the bladder and left urinary tract were nearly completely regressed after two cycles of systemic cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy with simultaneous restoration of urinary function.