We encountered 8 patients with primary carcinoma in situ of the bladder. All the cases had cystic irritation symptoms, and diagnosis was confirmed by urinary cytologies and transurethral biopsy. Total cystectomy was performed in 5 of the 8 cases during the course of disease. Bacillus Calmette-Guerin (BCG) instillation therapy was instituted in 4 cases, in two cases of which bladder malignancies were abolished after BCG instillation therapy. In one case treated by total cystectomy, histopathological study disclosed malignancies that invaded to the bladder musculature.