Urothelial cancer can be considered to consist of a spectrum of diseases with diverse natural histories and the conventional morphological classifications provided by classical histology remain the basis for any decision‐making process. The proliferative rate of the tumor cells may be significant since the rate of DNA synthesis is directly related to the rate of tumor growth or tumor involvement. We have previously reported that flow cytometric deoxyribonucleic acid (DNA)/bromodeoxyuridine (BrdU) bivariate analysis can provide important information about the malignant potential of bladder cancer. In the present study, we have formulated a new system based on the histological grade and tumor proliferative activity determined by the BrdU labeling index. An attempt has been made, moreover, to investigate whether this grading system can be used to determine the malignant potential of bladder cancers. A total of 86 patients with bladder tumors, histologically proven to be transitional cell carcinomas, were analyzed. Immediately after removal of tumor specimens,in vitroBrdU labeling was performed. Multivariate survival analysis was conducted using Cox's regression model, followed by estimation of the risk ratio for survival. Based on the risk ratio of the histological grade and the BrdU labeling index, a score ranging from 1 to 52 was assigned to each tumor. Forty‐four patients with a score of 1 had a 100% survival rate at 3 years, compared with 42.9% for patients having a score greater than 1. Conversely, 26 patients with the highest score, 52 exhibited a survival rate of only 17.3% at 3 years. These results suggest that the new grading system can be used as an indicator for making decisions about treatment in cases of transitional cell carcinoma of the blad