We sampled vole populations in Ukraine with the dual goal of characterizing population diversity and of providing a biogeographic perspective to evaluate experimental designs used for previous studies. Our data indicate that genetic diversity in bank vole populations is widely variable across regions and that diversity estimates in contaminated sites are unremarkable compared to those in uncontaminated areas. Furthermore, the relative frequencies of haplotypes have remained statistically identical throughout multiple sampling periods. Thus, the genetic data from bank vole populations in Ukraine fail to support the hypothesis that mutational changes in contaminated regions are the product of exposure to Chernobyl radiation. Our results suggest that genetic diversity in radioactive regions of Ukraine is probably a function of natural geographic variation rather than increased mutational pressure from radiation exposure and underscore the importance of adequate geographic sampling in studies designed to elucidate the effects of toxicant exposure.