Basic and clinical research has led to a better understanding of bladder tumor disease. Better characterization of host and tumor has made it possible for the clinician to choose appropriate treatment and follow-up and to better predict prognosis. Therefore, at tumor presentation a number of variables should be determined to reach the goal. Tumor factors: T-category, grade, size, number and appearance of the primary tumors, time to first recurrence and for invasive tumors also N- and M-categories, small vessel invasion, recurrence pattern, papillary stalk or true lamina propria invasion, the presence of secondary carcinoma in situ, ureteric obstruction and response to specific treatment. Host factors: Immune status, age, performance status, sex, pretreatment length of history and hemoglobin. However, in the individual patient bladder tumor disease may not always follow the predicted course, so that we are still in need of more accurate biological predictors. A number of markers (cytogenetic and cytomorphometric characteristics, such as flow-cytometry, immunohistochemical markers such as ABH expression, T-antigen, CEA, TPA and cytokeratins, and finally ultrastructural changes, proliferative indices and morphometric analysis) have been evaluated. Some have been shown to be of clinical value, but have as yet not been included into routine clinical use. Thus, we are steadily approaching the goal to disclose the true biological potential of each individual tumor and its relation to the host.