The epidemic/epizootic of West Nile (WN) encephalitis in the northeastern United States in the summer and fall of 1999 was an unprecedented event, underscoring the ease with which emerging infectious pathogens can be introduced into new geographic areas in today's era of rapid transportation and increased movement of people, animals, and commodities. This epidemic/epizootic and the increased frequency of other exotic pathogens being imported into the United States raises the issue of whether local, state, and national public health agencies are prepared to deal with epidemics/epizootics of vector-borne infectious diseases. The overwintering of WN virus and the epizootic transmission in the summer of 2000 reinforces the need to rebuild the public health infrastructure to deal with vector-borne diseases in this country. This article summarizes guidelines for surveillance, prevention, and control of WN virus that were drafted in December 1999 to help prepare state and local health departments for monitoring WN virus activity in the spring and summer of 2000 and also summarizes the data collected from those surveillance systems through September 2000.