Bladder and kidney cancer together account for about 5% of cancers worldwide, and represent the 9th and 14th most common cancers in terms of absolute numbers, respectively. Our knowledge of these two cancers, however, indicates that they have strikingly different etiology. A number of important occupational, lifestyle and genetic factors have been implicated in bladder carcinogenesis, which have greatly increased our understanding of this disease. In some instances, identification of these factors has contributed to the prevention or reduction of exposure to bladder carcinogens. Conversely, the etiology of kidney cancer is less well elucidated, which limits the possibilities for reducing its incidence by this approach. It is likely that much remains to be uncovered about the causes of these two cancers, and these advances will increase our appreciation of the biology of these cancers and perhaps lead to further possibilities for their prevention. In this article, we evaluate the epidemiology of bladder and kidney cancer and also discuss potential priorities for future research.