Lagidium ahuacaense is a rodent in the mountain viscacha genus (Lagidium) that occurs in southern Ecuador. First observed in 2005 and formally described in 2009, it occurs more than north of the nearest previously known population of mountain viscachas in central Peru. Only a single population is known, found on rocky habitats on Cerro El Ahuaca, an isolated granite mountain in southern Ecuador, and there may be as little as a few dozen individuals. The species is threatened by fires and grazing cattle, and the discoverers recommended its conservation status be assessed as "Critically Endangered".