Eulemur mongoz is a small member of the genus, with a head-body length of 30–35 cm, a tail length of 45–48 cm, an overall length of 75–83 cm, and a weight of 1.1–1.6 kg (Tattersall, 1982; Terranova and Coffman, 1995; Pastorini et al., 1998). The species is sexually dichromatic. In males, the dorsal coat is gray-brown and darker at the tip of the tail. There is also a darker pygal patch. The back of the neck and shoulders are often a rufous brown. The ventral coat is a paler creamy-gray. The muzzle and face are gray. The rufous cheeks and beard are the most distinguishing features of the male. A triangular bald patch on the top of the head sometimes results from excessive rubbing during scent-marking. In females, the dorsal coat is gray and lighter than that of the male, but females share the darker tail and dark gray pygal patch, as well as a lighter, cream-colored abdomen. The muzzle is light gray, the face a darker, slate gray that is surrounded by a white bushy beard that extends to the ears and reaches down the throat and onto the forelimbs. The eyes are reddish-orange in both sexes. North of the Betsiboka River this species is sympatric with the brown lemur, E. fulvus, which has a darker coat and is not sexually dichromatic. South of the Betsiboka River, E. mongoz is sympatric with the rufous brown lemur, E. rufus, with which it is unlikely to be confused, unless one gets only a fleeting glimpse of the animal. However, Zaramody and Pastorini (2001) report a small zone of hybridization between the two species. The mongoose lemur tends to be more cryptic in its behavior and lives in smaller groups than the other Eulemur species with which it is found. In the Comoros, where this species also occurs, it is the only lemur on the islands of Mohéli and Anjouan, and cannot be confused with any other species.