Head and body length is 382-635 mm and tail length from 508-890 mm. Weights average 6kg. and as much as 8 kg. for captive animals. The fur is coarse and stringy varying in color from yellowish gray, darker gray, reddish to dark brown to almost black above, sides are golden yellow to rufous and the underparts are lighter, usually whitish or yellowish. Most forms have a black face with white eyerings while others have a flesh-colored face.

Their arms and legs are exceptionally long in relation to the body and the tail is prehensile and very flexible which account for their extreme agility in the trees and rarely descends to the ground. The tail is used as a fifth arm as it swings through the branches. A. geoffroyi is found in rain and montane forest, seeming to prefer the small branches of the high strata of the canopy. They are entirely diurnal and feed intensively in the morning mainly on fruits. They also supplement their diet with nuts, seeds, buds, flowers, leaves, insects, arachnids and eggs.

When threatened they break off branches and throws them at the intruder. Vocalizations include a terrierlike bark when approached and a whinny like that of a horse when individuals become separated from the group. Home ranges vary in size from 150-250 hectares and overlap with other groups is about 10-15 percent. Females with infants tend to stay in the core area while males utilize the entire range. The number of individuals within a group varies considerably. Females sometimes emigrate to another troop, but males tend to stay with their natal group.

Estrous cycles are from 24-27 days and breeding occurs year round. Gestation is 226-232 days with a normal litter size of one. Females will generally have another offspring about 34.5 months later. Sexual maturity for females is reached at about 4 years and 5 years for males.

In general, they are vulnerable to hunting and habitat loss due to human activity. They are found from S Mexico to Panama.