A case of primary malignant lymphoma of the bladder is presented. A 42-year-old woman was admitted to our clinic with the chief complaint of asymptomatic hematuria. Examination of cystoscopy, IVP, ultrasonography and CT scan suggested a non-epithelial tumor of the bladder, which was reported as malignant lymphoma, non-Hodgkin, by findings of transurethral biopsy. Subsequent systemic CT scan, Ga-scintigraphy and bone marrow puncture revealed no abnormalities. Therefore, this case was thought to be primary malignant lymphoma of the bladder. Partial cystectomy with pelvic lymph node resection was carried out. The tumor, 2 x 1 cm in diameter, invaded into the middle portion of muscularis. Histological diagnosis of the tumor was follicular lymphoma, medium-sized cell type according to LSG classification, and immunohistological findings also showed B-cell lymphoma. Resected lymph nodes had no signs of neoplasms. Postoperative adjuvant chemotherapy consisting of vincristine, cyclophosphamide and prednisolone was performed. She has been doing well without any clinical evidence of recurrence for 16 months after the operation.