We assessed a situation concerning contracted bladder following intravesical instillation of BCG(Japan), to investigate how the disease could be prevented. Between March 1997 and June 2010, we selected 20 patients with clinically or pathologically confirmed contracted bladder to participate in the study. The incidence of contracted bladder tended to be higher for patients who had received more than 5 doses of BCG. Repeated severe bladder irritation caused by intravesical BCG instillation was suggested to be the major factor leading to contracted bladder. To prevent the onset of contracted bladder and its progression resulting in total cystectomy, BCG instillation should be discontinued in patients who have received the instillation many times and have developed persistent severe bladder irritation with significantly reduced bladder capacity. It is necessary to consider the administration of antituberculotic and steroid therapy for these patients quickly.