Our findings indicate that GIS can greatly enhance epidemiologic research in terms of definition of source and routes of potential exposure and estimation of environmental levels of target contaminants in the exposure assessment process. We found over 15 studies published since 1998 that describe the successful use of GIS for one or more of these purposes. Across all of these studies, there was consensus that the use of GIS was instrumental in achieving optimal exposure assessment. In our example studies, GIS improved resolution of the source of potential exposure (Elliott et al. 2001; Reif et al. 2003), identified the most likely route of exposure (Reif et al. 2003), and estimated levels of target contaminants for use in estimating exposure to the study population (Nyberg et al. 2000; Reif et al. 2003). Our examples of environmental epidemiology studies using GIS also emphasize the importance of interdisciplinary study teams.