Increasing knowledge in molecular genetic research on urinary bladder carcinoma has allowed us to classify the morphological picture on the basis of a better understanding. But this new knowledge will only be ground-breaking if it can be correlated with the clinical outcome of urinary bladder tumours and with histopathological findings. The use of the new 2004 WHO classification results in a standardized diagnosis of urothelial tumours by means of an exact definition of the subgroups. In the future, trials can thus be compared worldwide and risk profiles can be stratified. Further research in molecular genetics and correlation with the current classification together with molecular biological techniques may allow refinement of this scheme, e.g. by immunohistochemical subclassifications, enabling identification of potentially genetically unstable tumours. In this paper we present the new 2004 WHO classification of urinary bladder tumours emphasizing the changes in relation to the former classifications focusing on histological typing, grading and molecular characterization. Until the new classification is finally validated, and those working in the field have become familiar with it, the WHO classification of 1973 should be mentioned additionally in the histopathological report.