Urinary bladder cancer has long been associated with specific etiologic factors, and our knowledge of these factors has increased during this century. The most important factor, even in industrialized societies, is cigarette smoking. Specific chemicals have also been identified as causing bladder cancer, as have a variety of occupational exposures to less well-defined specific agents. In other parts of the world, the association of bladder cancer with Balkan nephropathy, endemic blackfoot disease, and schistosomiasis provides additional leads for investigating, and potentially preventing, the process of carcinogenesis in humans. Many of the critical observations in our understanding of bladder cancer have been made by practicing physicians, and this is likely to continue. It is essential that physicians dealing with bladder cancer patients be attuned to potential etiologic factors, including cigarette smoking, various industrial exposures, or drug exposures to further our understanding of this issue. Bladder cancer is a potentially preventable disease and an important one, as indicated by the total number of cases and the extent of morbidity and death attributable to it around the world.