Transitional cell carcinoma involving the prostate in patients with bladder carcinoma impacts on the judicious use of intravesical chemotherapy, partial cystectomy and internal urinary reservoirs anastomosed to the urethra. We compared the accuracy of prostate needle biopsy, fine needle prostatic aspiration and transurethral resection biopsies of the prostate to detect the presence or absence of transitional cell carcinoma involving the prostate in 25 men undergoing radical cystectomy, of whom 40 per cent had transitional cell carcinoma of the prostate. The accuracy of the 3 detection methods was 20, 40 and 90 per cent, respectively. If any 1 of the 3 tests was positive all patients with transitional cell prostatic cancer were correctly identified. These tests should be performed in high risk patients, including those with transitional cell carcinoma in situ of the bladder, or with a positive urine cytology study and a cystoscopically as well as biopsy proved normal bladder urothelium.