Worldwide, an estimated 261 000 cases of urinary bladder cancer are diagnosed, and result in 115 000 deaths each year. Strong evidence exists for an association between bladder cancer and exposure to arsenic (As) in drinking water at concentrations exceeding 300–500 μg/l; however, health risks from As exposure in the 10–100 μg/l range are equivocal. Given low-to-moderate concentrations of As in drinking water, other sources of As exposure such as food, occupational hazards, and tobacco may be important. Exposure to other potential bladder carcinogens in drinking water, such as disinfection byproducts or nitrates, along with mediating factors in the diet, such as selenium and zinc, may also prove to be decisive factors. This review presents a critical evaluation of epidemiologic studies of As in drinking water and bladder cancer, emphasizing the need to carefully assess individual-level exposure to As in drinking water along with other sources of As, as well as considering potential confounding and mediating factors.