A new species of tuco-tuco, genus Ctenomys , is described from Chilean Patagonia. Multivariate analyses of external and cranial measurements discriminate between this and the allopatric C. colburni . Chromosomal and qualitative cranial characters confirm the specific distinction of the new taxon (2n = 28). Although morphologically most similar to neighboring C. colburni (2n = 34), chromosomal data indicate that the new taxon is more closely allied with the C. maulinus group (2n = 26). Diagnostic characters of the new species include relatively small size, silvery-white hairs on the dorsal surface of the hind feet, a roughly linear alisphenoid-presphenoid bridge, a single large lateral alisphenoid foramen, and a round and large post-alisphenoid canal.