The name of the first species sometimes is spelled L. lagothricha. Among American monkeys this genus is exceeded in weight only by some Alouatta and Brachyteles and in length by some individuals of Ateles, with their very long tails. The hair is short, thick, and woolly, with a good growth of underfur. The upper parts are hoary gray, blue gray, tawny, dark brown, or blackish brown, and the underparts are only slightly lighter.
Some individuals are yellowish buff.
The naked face is almost black. Woolly monkeys have a round and massive head, a relatively heavy body for tree monkeys, and a tail that is bare on the undersurface for several millimeters near the tip and prehensile. The thumbs and toes are well developed, and the fingers are short and thick with long pointed nails. In Colombia Lagothrix lives in gallery forests, palm forests, flooded and nonflooded primary forest, and cloud forest as high as 3,000 meters but not in secondary forest. It seems to be less active in the wild than most American tree monkeys, and it definitely is less active in captivity.