© 2015 Wayne State University Press, Detroit, Michigan 48201. Molecular-based characterizations of Andean peoples are traditionally conducted in the service of elucidating continent-level evolutionary processes in South America. Consequently, genetic variation among “western” Andean populations is often represented in relation to variation among “eastern” Amazon and Orinoco River Basin populations. This west-east contrast in patterns of population genetic variation is typically attributed to large-scale phenomena, such as dual founder colonization events or difffering long-term microevolutionary histories. However, alternative explanations that consider the nature and causes of population genetic diversity within the Andean region remain underexplored. Here we examine population genetic diversity in the Peruvian Central Andes using data from the mtDNA fĳirst hypervariable region and Y-chromosome short tandem repeats among 17 newly sampled populations and 15 published samples. Using this geographically comprehensive data set, we fĳirst reassessed the currently accepted pattern of western versus eastern population genetic structure, which our results ultimately reject: mtDNA population diversities were lower, rather than higher, within Andean versus eastern populations, and only highland Y-chromosomes exhibited signifĳicantly higher within-population diversities.