A case of non-specific granulomatous prostatitis is reported. The patient, who had a history of sudden onset of high fever and acute urinary retention, had a hard prostate on digital rectal examination that gave us an impression of prostatic cancer. Since repeated biopsy specimens from the prostate showed granuloma formation with fibrinoid necrosis, the case was diagnosed as non-specific granulomatous prostatitis. Steroid therapy promptly resolved clinical symptoms along with marked histopathologic improvement.