Effectively dealing with the rapid evolution and diffusion of modern viruses and diseases requires the implementation of large-scale health surveys and studies. Geographic Information Systems (GIS) allow for the efficient monitoring and tracking ofviruses and diseases throughout large geographic areas This paper details the advantages of using a GIS in large-scale medical surveys through a review of Pennsylvania's West Nile Virus Surveillance Program. Current and future applications of GIS related to this mosquito-borne pathogen, such as cartographic representations of the threat and the ability to predict future areas of concern, are among the issues discussed. These applications demonstrate the capability of GIS for computerized mapping and, more importantly, as a set ofspatial analysis tools that can be utilized for important medical-related decision making.