A new species of lizard of the genus Liolaemus from southwestern Rio Negro Province, central Patagonia is described. The new species is a member of the Liolaemus fitzingerii group, and molecular data show it as sister taxon of L. martorii, but it differs in size, squamation, coloration, and sexual dimorphism. Liolaemus casamiquelai sp. nov. is terrestrial, dwelling on loose sandy soil in a shrubby landscape, and seems to be oviparous and insectivorous.