in common with other callitrichides (tamarins and marmosets), geoffroy's tamarin is a small monkey. with a length of between , excluding the tail, it is the smallest central american monkey. the tail length is between . males have an average weight of , and females are slightly larger on average, with an average weight of . the fur on its back is variegated black and yellow, with pale legs, feet and chest. its face is nearly bare, but the head has reddish fur with a triangle-shaped patch in the front of the head. the tail is chestnut-red and has a black tip.