Aedes vexans is a potential vector of West Nile Virus, dog heartworm, and St. Louis encephalitis, Rift Valley Fever Virus, and has a widespread distribution throughout the world including the continental U.S. and southern Canada. Population genetics of this mosquito was investigated in the U.S., and in selected locations worldwide. Over 100 adult mosquitoes were examined using a portion of mitochondrial NADH dehydrogenase subunit 5 (ND5) gene. Aproximately ten mosquitoes per location were examined. This study supports evidence of high genetic diversity in Neartic and Paleartic regions. Some level of gene flow across locations is also supported due to the presence of limited haplotypes in different locations. Populations of this mosquito species are also in constant growth. KEY WORDS Aedes vexans, mitochondrial DNA, genetic variation