Arsenic is a ubiquitous environmental toxin with known neurological consequences. Few studies, however, have investigated groundwater arsenic concentrations and cognition among adults and elders. In the study described in this article, the authors examined the potential link between cognitive functioning and low concentrations of arsenic in drinking water. Arsenic concentrations were estimated by the Geographic Information System approach (GIS-arsenic) for 299 rural-dwelling adults and elders. Cognition was assessed with Folstein Mini-Mental State Examination (MMSE). Those in the relatively high GIS-arsenic exposure (> 10.0 microg/L) group had significantly lower MMSE scores than those in the low GIS-arsenic exposure (< or = 10.0 microg/L) group (p < .03). The number of years of education was significantly lower in those in the high GIS-arsenic group(s) than in those in the low GIS-arsenic group (p < .05). These results suggest that poorer cognitive functioning and lower education levels were associated with higher (though still low-level) GIS-arsenic levels in this rural adult cohort.