Studies on the innervation of the sternocleidomastoid muscle have shown the highly variable arrangement of the nerve fibers originating from the accessory nerve (eleventh cranial pair) and cervical nerves which supply the muscle. The results of 100 dissections described in this study confirmed these variations and led to propose a classification of the innervation of the sternocleidomastoid according to three main types. The classical "anastomotic" type of innervation (also referred to as Maubrac's type of innervation) was the most frequent, although present in only half of all cases. Innervation of the sternocleidomastoids in symmetrical fashion was an exceptional finding. The functional attributes of these anatomical variations are discussed.