A total of 13 patients received intravesical bacillus Calmette-Guerin (BCG) therapy for superficial bladder cancer and were followed for at least 6 months (range 6 to 50 months). Of the patients 7 had carcinoma in situ and 6 had recurrent tumors following intravesical mitomycin C therapy. Of the 7 patients who had carcinoma in situ, 4 (57%) are free of disease and 3 (43%) have required cystectomy for recurrence or progression. Of the 6 patients who had recurrent tumors following intravesical mitomycin C therapy, 3 (50%) remain free of tumor after BCG therapy alone, 2 (33%) had superficial recurrences but no progression and 1 (17%) has required cystectomy for prostatic involvement. After intravesical BCG therapy, transitional cell carcinoma of the prostate was identified in 4 of the 13 patients, and tumors in the upper urinary tract were detected in 2 of the 4 patients with prostatic involvement. Of the 4 patients 2 have local recurrence or distant metastasis. In patients treated with BCG therapy the prostate and upper urinary tract represent a potential site of progression or recurrence. Patients treated with intravesical BCG therapy for superficial bladder cancer should be monitored closely for the development of transitional cell carcinoma of the prostate and upper urinary tract.