The head is small and the muzzle substantial. The upper fur is black, brown, or reddish and the face is often marked with a pale mask of unpigmented skin around the eyes and muzzle. These monkeys eat mainly ripe friut and less frequently leaves and flowers. Reproduction Ateles geoffroyi does not appear to have a regular breeding seaseon. Gestation lasts 226 to 232 days and one young is born.
Ovulation is suppressed by lactation and births occur at two to four year intervals.
Males are sexually mature in five years and females in four. These animals are social and tend to form groups of approximately thirty individuals. Groups of up to 100 have been reported. For the most part, these large groups split into smaller subgroups to forage and only for a few weeks out of the year is the whole group together. Group size varies with habitat type and seems to depend largely on the productivity of the area.