There are two subspecies of drill. Drills are dark brown with a black face, white tufted beard and scarlet lower lip. They have a long muzzle with lateral ridges. Their hindquarters is naked and varies in color, which range from bright red, blue, and light purple to lilac and pink. Inner thighs are red.
Males are larger and more colorful than females.
Their skulls show a marked sexual dimorphism. Males average 28 inches in length and weigh around 37.5lbs. Adult mandrill males are larger and more colorful than females. Their long snouts are red and blue and they have yellow-orange beards. They also have colorful rumps, which are thought to aid drills and mandrills in leading their groups through dense forests.