European treatment guidelines of non-muscle-invasive urothelial carcinoma of the urinary bladder are strongly dependent on grade, but grading reproducibility is wanting. Protocolized proliferation features such as Mitotic Activity Index (MAI), Ki-67, and phosphohistone H3 are prognostic and reproducible. The objective of this population-based study was to compare proliferation biomarkers with each other and with World Health Organization (WHO) 1973/2004 grades with regard to prediction of stage progression. A total of 193 primary non-muscle-invasive urothelial carcinomas were analyzed using WHO73/04 grades and measurement of the proliferation markers mentioned above. Sensitivities, specificities, and positive and negative predictive values with confidence intervals (CIs) were estimated with regard to progression prediction. Kaplan-Meier survival curves were made, and the hazard ratio and Harrell's C-index with 95% CIs, P values, and adjusted C-index for stage progression or not of WHO73, WHO04, and the proliferation markers were calculated. The median follow-up time was 75 months (range, 1-127). A total of 111 patients (52%) experienced recurrence within 5 years, and 14 patients (7%) progressed. High values of MAI predicted stage progression with a positive predictive value of 0.22 (95% CI, 0.12-0.37). The positive predictive value of Ki-67 and phosphohistone H3 were 0.15 (both 95% CIs, 0.07-0.29) and comparable to that of the WHO04. The prognostic value of MAI was strongest, exceeding that of the other proliferation markers and the WHO grading systems. In conclusion, in non-muscle-invasive urinary bladder urothelial carcinomas, proliferation biomarkers have prognostic value, possibly exceeding that of the WHO classifications.