A new species of treefrog is described from the central region of the Western Sierra Madre del Sur of Guerrero, Mexico. This frog is a member of the genus Charadrahyla, which contains five other species that are restricted to mesic highlands in Mexico. It possesses extensive webbing and in particular a hypertrophied membrane between toes I and II. This characteristic distinguishes the species from all other Middle American hylid frogs, except C. trux that also occurs in Sierra Madre del Sur of Guerrero. From C. trux the new form differs in being smaller, having relatively longer legs, aspects of coloration, and in having more prominent cloacal ornamentation.