Water supplies in many parts of the world contain naturally occurring arsenic. Previous studies have shown that arsenic at high doses can cause cancer of the bladder. The risk at lower doses is unknown. This study is examining the relationship between ingested arsenic and bladder cancer in central Nevada and Kings County, California, two areas where a large percentage of the population was exposed to drinking water containing arsenic at low to moderate levels. Approximately 200 people with bladder cancer and 400 people without bladder cancer will be included. Subjects are interviewed by telephone about past residences, occupations, diet, drinking water consumption, and other lifestyle factors. Arsenic measurements in well water have been collected from the appropriate state agencies and are being matched with residences and drinking water consumption rates to estimate lifetime arsenic exposures for each subject. People with bladder cancer will then be compared to those without to see if people with cancer were more likely to have lived in areas with arsenic in their drinking water.