The Andean Cordillera is notable for numerous centers of avian endemism along its great length. Yet, the narrow band of humid montane forest in eastern Ayacucho in south-central Peru is not known to harbor endemic bird species despite its position between two putative biogeographic barriers: the arid Apurímac and Mantaro river valleys. We report the first documented records of the endemic Ayacucho subspecies of Vilcabamba Thistletail, Asthenes vilcabambae ayacuchensis since its initial discovery and collection in 1968–1970. Unexpectedly, the previously unknown song of A. v. ayacuchensis is more similar to Eye-ringed Thistletail Asthenes palpebralis of Junín Department than to nominate A. v. vilcabambae of western Cuzco Department. Phylogenetic analyses of DNA sequences reinforce vocal evidence, and support that A. v. ayacuchensis is more closely related to A. palpebralis and the Rusty-fronted Canastero A. ottonis than to A. v. vilcabambae. Based on distinct vocalizations, phylogeny, and diagnosable plumage characters, ayacuchensis merits species recognition. The “Ayacucho Thistletail” is documented certainly from elfin forest localities in three small valleys in the Apurímac drainage in eastern Ayacucho. There are no protected areas or reserves that overlap A. ayacuchensis’ limited distribution and we suspect that it, like many elfin-forest specialists in the Andes, is threatened by anthropogenic habitat modification.