In the Ba Men region of Inner Mongolia, China, a high prevalence of chronic arsenism has been reported in earlier studies. A survey of the arsenic contamination among wells from groundwater was conducted to better understand the occurrence of arsenic (As) in drinking water. A total of 14,866 wells (30% of all wells in the region) were analyzed for their arsenic-content. Methods used to detect arsenic were Spectrophotometric methods with DCC-Ag (detection limit, 0.5 mug of As/L); Spot method (detection limit, 10 mug of As/L); and air assisted Colorimetry method (detection limit, 20 mug of As/L). Arsenic-concentrations ranged from below limit of detection to 1200 mug of As/L. Elevated concentrations were related to well depth (10 to 29 m), the date the well was built (peaks from 1980-1990), and geographic location (near mountain range). Over 25,900 individuals utilized wells with drinking water arsenic concentrations above 20 mug of As/L (14,500 above 50 mug of As/L-the current China national standard in drinking water and 2198 above 300 mug of As/L). The presented database of arsenic in wells of the Ba Men region provides a useful tool for planning future water explorations when combined with geological information as well as support for designing upcoming epidemiological studies on the effects of arsenic in drinking water for this region. [Authors]