Approximately 49,000 persons in the United States develop bladder cancer each year, and about 9700 die of it. White men face a lifetime risk of almost 3%; white women and black men face a risk of about 1%, and black women, about 0.5%. Cigarette smoking is accepted widely as a cause of bladder cancer. Smoking accounts for about half of bladder cancer diagnosed among men and about one third of that among women. Moderate to heavy smokers typically show a two to five fold risk of bladder cancer, compared with persons who never smoked. When cigarette smokers quit smoking, their bladder cancer risk falls measurably within 2 to 4 years, but probably does not continue to decline with increasing years since quitting and does not appear to return to the baseline level of nonsmokers. Occupational exposure to certain aromatic amines causes human bladder cancer. Clear evidence of bladder cancer risk also is apparent for a small number of occupational groups: dye workers, rubber workers, leather workers, painters, truck drivers, and aluminum workers. Many other occupational groups have been reported to have increased bladder cancer risk, but evidence for these is not as strong. Coffee drinking has been studied extensively as a potential risk factor, but the inconsistency of the observed associations suggests that the relationship is either quite weak, noncausal, or dependent in a complex way on unmeasured factors. Artificial sweeteners confer little or no excess bladder cancer risk. Alcohol consumption apparently does not affect risk either. Consumption of fruits, vegetables, and foods high in vitamin A have been suggested as possible protective factors; consumption of high-fat foods, pork, and beef have been suggested as possible risk factors. Further epidemiologic research is needed to elucidate the role of diet in human bladder carcinogenesis. Less common risk factors for bladder cancer include ionizing radiation, cyclophosphamide use, and abuse of phenacetin-containing analgesics. Schistosomiasis infection may contribute substantially to the bladder cancer burden in Egypt and elsewhere, though not in the United States.(ABSTRACT TRUNCATED AT 400 WORDS)