Thirteen Aedes hexodontus Dyar populations from throughout the western United States were examined for genetic and morphological variation. Analysis of allozyme frequencies at 16 loci revealed a pattern of genetic variation that formed a north-south cline across Washington, Oregon, and California in the number of alleles per locus, the percent of polymorphic loci, and the frequency of one allele of aconitase-1. Comparison of the genetic profile of Ae. hexodontus populations to two other widely distributed members of the punctor subgroup, Aedes punctor (Kirby) and Aedes abserratus (Felt & Young), revealed only one diagnostic locus for all three species. Seven loci exhibited frequency differences among species but were not diagnostic. Morphological characters also exhibited little variation within and among the three species. The adult females differed only in the scaling of the probasisternum. This area was extensively scaled in 91% of Ae. hexodontus specimens but bare or only lightly scaled in Ae. puntor and Ae. abserratus. No other differences were observed in the adult females or the male genitalia in any of the three species. The larvae of Ae. abserratus could be separated by the single-branched seta 2-X. Six larval characters differed between Ae. hexodontus and Ae. punctor but the ranges of each character overlapped and none were diagnostic. These comparisons indicated that Ae. hexodontus is a single species, at least in the southern part of its range. Also, genetic and morphological comparison of the three species within the punctor subgroup attested to the close relationship hypothesized for these mosquitoes.