The sternocleidomastoid is a muscle with a great extension that occupies the cervical region and is extended obliquely from the head to the trunk. Its morphology is not uniform, once its ends are wide and slim while its medial edge is thick and narrow. The aim of our work was to relate a case of variation in clavicular origin of this muscle that was extended beyond the half of clavicle laterally, in both sides of the neck.