We used a comparative, multimarker approach to investigate the conservation genetics of an arboreal vole (the Sonoma tree vole [Arborimus pomo]) in the Pacific Northwest of North America. We compared geographic patterns and overall levels of genetic diversity based on 55 amplified fragment length polymorphism (AFLP) loci with those based on a single, commonly used mitochondrial locus, the control region. Although examination of the control region data revealed the presence of 2 distinct mitochondrial DNA (mtDNA) clades within A. pomo (1 in the north and 1 in the south of the species' range), the nuclear perspective provided by AFLP did not reveal a similar geographic division within the species, supporting instead that A. pomo consists of a single panmictic population. Genetic diversity estimates based on the mtDNA data (gene diversity = 0.79 and 0.80 for the 2 clades) were much greater than those based on AFLP (gene diversity = 0.31 and 0.19 for the 2 clades). These contrasting results reflect inherent differences between mitochondrial and nuclear loci in mutation rate, effective population size, expected time to monophyly, and mode of inheritance, and highlight the utility of using the combination of AFLP and mtDNA when assessing the genetic status of wild populations and species of mammals, especially those of conservation concern. In the case of A. pomo, our combined AFLP and mtDNA data support the recognition of the southern Sonoma tree voles as a distinct management unit within the species.