Granulomatous prostatitis is an uncommon condition that can masquerade as prostatic carcinoma on both digital rectal exam and prostate ultrasound. It occurs most often after acute urinary tract infection, transurethral prostate resection, or needle biopsy. It can be seen in systemic granulomatous diseases and after intravesical bacillus Calmette-Guerin (BCG) therapy for bladder carcinoma. In some cases it is idiopathic. Six patients who underwent transrectal ultrasound of the prostate and subsequent transrectal ultrasound-guided biopsy had histologic diagnosis of granulomatous prostatitis. One patient was undergoing BCG therapy for bladder cancer. Two patients had recent urinary tract infections. The other three patients had no known predisposing conditions. Sonographically, the glands were enlarged in five patients, with multiple large and small hypoechoic zones throughout the peripheral, transition, and central zones. The appearance was similar to that seen in diffuse prostatic carcinoma. In one patient, a solitary hypoechoic lesion in the peripheral zone, indistinguishable from carcinoma, was present. Granulomatous prostatitis should be considered in the differential diagnosis of focal and diffuse abnormality with prostatic ultrasound.