A new lizard of the genus Liolaemus is described from the Tacna region of southern of Peru. This species belongs to the L. montanus group and was initially thought to be L. poconchilensis and L. insolitus. However, a series of diagnostic characters differentiate it consistently from these two species and all other species of the genus. To determine the taxonomic status of these lizards, their phylogenetic relationships were analyzed, as well as their morphological and ecological characteristics. The results of the analysis support the conclusion that this population of lizards represents a new species to science, and that the new species is related to L. nazca and L. chiribaya. The new species has sexual dimorphism and is known from elevations of ca. 1,000 m above sea level in the hyperarid Pacific deserts, which are populated by scattered Ephedra americana and Poissonia sp. Due to its highly restricted range and observed habitat loss, we recommend this species be categorized as Critically Endangered.