Intravesical bacillus Calmette-Guérin (BCG) immunotherapy is a common treatment modality for bladder cancer after transurethral resection of a bladder tumor. This therapy is generally safe, and development of a prostatic abscess with a prostatorectal fistula after intravesical BCG immunotherapy is a very rare complication. This finding was incidentally obtained by the authors, who examined a patient with colonoscopy for evaluation of abdominal pain. The patient was successfully treated with antitubercular drugs. To the authors’ knowledge, this is the first report of a patient with a tuberculous prostatic abscess with prostatorectal fistula after BCG immunotherapy in South Korea.