A 72-year-old man visited a hospital because of a fever and fatigue. His fever persisted and computed tomography revealed a tumor of the prostate. The patient was referred to our hospital with a suspicion of prostate cancer. The blood test showed increased serum C-reactive protein (CRP) level without any infectious findings. Tumor markers including prostate specific antigen were within the normal range and urine cytology was negative. Prostate needle biopsy revealed urothelial carcinoma. No tumor was detected in other areas of the urinary tract. Therefore we diagnosed the patient with primary urothelial carcinoma of the prostate, cT3N0M0. Serum interleukin-6 (IL-6) elevated up to 68 ng/ml. We were not able to detect any metastatic lesions and performed radical cystoprostatectomy and ileal conduit. Serum CRP and IL-6 levels decreased and the fever declined. There has been no relapse 52 months after the surgery.