We report 3 cases of prostatic involvement of transitional cell carcinomas (TCCs). All cases presented positive urinary cytology after intravesical instillation of Bacillus Calmette-Guerin (BCG) and then random biopsy of bladder and transurethral resection (TUR)-biopsy of prostatic urethra were performed. TUR-biopsy demonstrated TCC in the prostate, although random biopsy failed to detect tumors in the bladder in all cases. Case 1 was treated with cystourethrectomy with ileal conduit, case 2 was treated with cystourethrectomy with bilateral ureterocutaneostomy and case 3 was treated with cystectomy with orthotopic ileal neobladder reconstruction. All cases are alive with no evidence of disease. TUR-biopsy of prostatic urethra should be perfomed when patients present positive urinary cytology after BCG instillation therapy, because prostatic involvement of TCC associated with bladder carcinoma in situ is not rare.