The average body mass for an adult male drill is around 20 kilograms and for adult females it is 12.5 kilograms (Hill, 1970; Fleagle, 1999). The drill has a dental formula of 2:1:2:3 on both the upper and lower jaws (Ankel-Simons, 2000). The drill, like all cercopithecines, has cheek pouches for storing food while foraging. The dorsal pelage color is olive-green, with the face and ears being black. The ventral side is colored white or gray-white (Groves, 2001). The anterior region of the scrotum of the male is colored pink and the posterior region is a lilac color. The region around the anus is colored red. The bright color of the skin will become more pronounced when an individual is excited (Nowak, 1999). The glans penis of the male is colored pink. Infants are born with a distinctive light colored face that darkens to black at 8 months (Boer, 1987). This is a sexually dimorphic species. There are swells on either side of the nasal area, pronounced maxillary ridges.
This species has two subspecies each having slightly differing pelage colorations: