OBJECTIVE We determined whether patients with bladder cancers accompanied by carcinoma in situ (CIS) or epithelial dysplasia carry a poor prognosis. METHODS The resected bladders from 57 patients with a bladder cancer were step-sectioned. The stained specimens underwent microscopic examination and the extent of CIS and epithelial dysplasia was mapped out. The 57 patients were followed up for 5 to 10 years and the cumulative survival rates were calculated. RESULTS Gross tumors were accompanied by CIS in 29 (51%) patients and by epithelial dysplasia in 52 (91%) patients. The survival rates did not differ significantly between the presence and absence of the accompanying mucosal lesions. However, the cancer specific survival rates were higher in patients with accompanying CIS located away from the gross tumor than in patients with CIS located adjacent to the gross tumor (p = 0.04). In patients with a non-papillary bladder cancer the survival rates tended to be higher when accompanying epithelial dysplasia accounted for over 3% of the whole mucosal area than when it accounted for less than 3% (p = 0.09). CONCLUSIONS These results suggest that the presence of accompanying CIS or Epithelial dysplasia does not indicated a poor prognosis, and may indicate a favorable prognosis in patients with a non-papillary bladder cancer.