Bighorn Sheep is a moderately large ungulate with a stocky body, a light to dark brown coat, and a large, conspicuous white rump patch. At the end of winter, the coat colour may be bleached lighter. The short tail is black; a black to dark brown tail stripe runs from the base of the tail to the upper edge of the patch. The end of the muzzle, the inside of the ears, the belly and the posterior sides of the legs are white. An adult male’s scrotum is readily noticeable because it is white and large relative to the body size. A small, black antorbital gland is visible at the front corner of each eye; its other glands are anal, caudal, inguinal and interdigital. Females have a pair of teats.
Both sexes have brown horns with transverse ridges and ripples along the surface. The horn sheaths of adult males are characteristically massive, steeply tapered from base to tip, and grow in a spiral, completing a full circle or more in some older males; but the horns of older animals may become broomed, where they lose the tips. The outer edge of the horn forms a prominent keel, and at the base, the horns of mature males are roughly triangular in cross-section. Compared to those of adult males, horns of adult females are much shorter and narrower. They have blunt tips and are oval in cross-section, curving gently up and backwards from the top of the head.