Urothelial tumors of the renal pelvis and the ureter do not differ from those of the urinary bladder concerning histopathological phenotypes. However, with respect to tumor biology there are relevant differences between the two tumor locations. The originating tissue (urothelium) of the bladder and of the upper urinary tract varies significantly with respect to developmental origin, morphology and physiological function. Specific pathways of tumorigenesis (e.g. hereditary non-polyposis colorectal cancer, HNPCC) and tumor propagation (seeding) are described for tumors of the upper urinary tract. Clinical epidemiological data indicate specific correlations between the two tumor locations.