Alouatta caraya are sexually dimorphic where males average 6.7 kg and females average 4.4 kg. Male body size ranges from 1.7 to 2.2 ft with tails of similar length to their body. Females' bodies average 1.6 ft with tails slightly longer than their bodies. Alouatta caraya are also sexually dichromatic. Males usually have black hair, which gives the species the common name of Black Howler monkey. Females however have more yellow-brown or olive colored hair. Infants are born with a golden coat, which changes as the animal matures. Alouatta caraya have long, strong prehensile tails. These tails are hairless on the underside, which allows them to be sensitive to touch and act in identifying things, much like a 5th hand. The black face is mostly hairless as well, with slightly bushy eyebrows. Alouatta caraya have brown, medium sized eyes set in a frontal position. The muzzle is prominent and the nostrils close together. Like other howlers they have enlarged hyoid and larynx housing the vocal apparatus where the distinctive howling originates. Alouatta caraya however, have less prominent lower jaw and bulging neck than some howlers.

(Welker et al. 1990, Walker et al. 1999, Bicca Marquez and Calegaro Marquez 1998)