A retrospective study was done including 265 patients with a mean clinical follow-up of 10 years. The mitotic activity in initial bladder tumor biopsies was estimated using two different methods: the traditional mitotic activity index (MAI) and the recently introduced volume-corrected mitotic index (M/V index). The grading results obtained using these indexes were compared to prognostic information obtained by subjective histological grading (WHO) and clinical staging (UICC). The progression of bladder cancer during the follow-up period was significantly related to the M/V index (p less than 0.0001), MAI (p less than 0.0001) and histological grade (p less than 0.0001) in that order. The progression in Ta-T1 tumors was significantly related to the M/V index in univariate and multivariate analysis as well. The recurrence-free period was significantly related to MAI (p = 0.006) and M/V index (p = 0.032). Clinical stage (p less than 0.0001), histological grade (p less than 0.0001), M/V index (p less than 0.0003) and MAI (p less than 0.0001) predicted bladder cancer-related survival. In a multivariate analysis the M/V index predicted the progression and survival better than MAI and gave comparable results to those obtained with subjective histological grading. The results encourage the use of the M/V index in grading bladder cancer in place of MAI.