In a retrospective study, staging and grading of 2085 primary and recurrent urinary bladder carcinomas were determined according to WHO and UICC rules. Of the carcinomas 51% were papillary, 23% solid and 26% partly papillary and partly solid. 46.2% of carcinomas were correspondent to malignancy grade I, 37.7% to grade II and 16.1% to grade III. The depth of invasion was the greater the less the degree of differentiation. The uncorrected recurrence rate of carcinoma was 14.9%, 28% of the recurrences showed an increase in malignancy grade and (or) depth of invasion. The recurrence rate fell within the first three years from 76.8% to 8.2%. In addition, there was a high degree of coincidence between carcinoma grade III and severe urothelial dysplasia. The diagnosis of severe dysplasia is an indication for frequent cystoscopic and bioptic checks. Since the biological significance of urinary bladder carcinoma depends not only on the degree of malignancy but also on the depth of invasion and the readiness of carcinoma towards invasion, it is necessary for successful prospective studies, designed to evaluate the course of urinary bladder carcinoma and their therapeutic response, to incorporate exact staging and grading.