Bacillus Calmette-Guerin (BCG) instillation therapy is now a standard therapy for high-risk superficial bladder cancer patients. Although the complete response rate is approximately 70%, extra-vesical progression is sometimes observed. In particular, those patients who present a positive urinary cytology even after complete response from bladder lesion should be thoroughly examined. We present two cases of stromal invasion of the prostate after complete remission by BCG therapy of carcinoma in situ of the ureter and bladder found by transrectal prostate biopsy.