As presently recognized, the genus Galea is composed of 3 species, G. musteloides, G. flavidens, and G. spixii. The most widely distributed species is G. musteloides (the common yellow-toothed cavy), ranging from southern Peru to southern Argentina and from sea level to over 4,000 m elevation. Our current taxonomic and systematic understanding of Galea is based primarily on morphological studies that have been limited in both taxonomic and geographic sampling. In this study phylogenetic analyses of sequences from the cytochrome-b gene were used to test hypotheses related to the content, limits, and systematic relationships within G. musteloides. Our data support restricting G. musteloides to the highlands of northwestern Bolivia, southeastern Peru, and extreme northeastern Chile. We elevate G. leucoblephara Burmeister, 1861, for populations occupying the lowlands of Bolivia and Paraguay to central Argentina, and we elevate G. comes Thomas, 1919, for populations from the Andes of southern Bolivia and northern Argentina. Our results also suggest the presence of a previously unrecognized form at midelevations in the southern Bolivian Andes. We find support for treating G. spixii campicola as a junior synonym of G. l. demissa and G. monasteriensis as a junior synonym of G. musteloides boliviensis. Most of the evolution of the taxa within the G. musteloides complex appears to have occurred in the Prepuna biogeographic province, with 2 independent vicariant events culminating in the separation of the G. musteloides, G. comes, and G. leucoblephara clades. Dating estimates suggest a late Miocene divergence between G. spixii and the G. musteloides group, followed by species-level divergence within the G. musteloides group during the Pliocene.