During July 2000-January 2002, the Wisconsin Division of Public Health conducted a study in 19 rural townships. A high percentage of private drinking-water wells in these townships contained traces of arsenic. Residents were asked to collect well-water samples and complete a questionnaire regarding residential history, consumption of drinking-water, and family health. In total, 2,233 household wells were tested, and 6,669 residents, aged less than one year to 100 years, provided information on water consumption and health. The well-water arsenic levels ranged from less than 1.0 to 3,100 microg/L. The median arsenic level was 2.0 microg/L. The arsenic levels were below the federal drinking-water standard of 10 microg/L in 80% of the wells, while 11% had an arsenic level of above 20 microg/L. Of residents aged over 35 years, those who had consumed arsenic-contaminated water for at least 10 years were significantly more likely to report a history of skin cancer than others. Tobacco use was also associated with higher rates of skin cancer and appeared to synergize the effect of arsenic on the development of skin cancer.