The sternocleidomastoideus muscle is one of the most complex muscles of the body. A wide mention of supernumerary and accessory musculature has been made in the literatures. In majority of cases, accessory muscles are asymptomatic and usually incidental findings at surgery or imaging. The objective of this study was to determine the prevalence of additional head of sternocleidomastoideus muscle, describe an anatomical variation of bilateral sternocleidomastoideus anatomy and review the clinical and surgical significance. A total of 16 cadavers of both sexes (15 men and 1 women) with different age group were used for the study. Head and neck region (32 sides) of the cadavers were carefully dissected as per the standard dissection procedure in the Morphology Laboratory at the University of Pamplona. The morphological variations in the number of heads (three and four) of origin of sternocleidomastoideus muscle were observed in 2 out de 16 neck (12,5%). It was found in two male subjects in right and left neck, bilaterally. The remaining 14 neck (87,5%) showed the normal origin, insertion, course of the sternocleidomastoideus and the course and branching patterns of the spinal accessory nerve and arterial patterns was normal having classic branching. The Knowledge of the presence of additional heads of Sternocleidomastoideus muscle is the interest why may cause functional deficits since its covers the important neurovascular structures of the neck; it might cause difficulties in the surgery in that region. It may also interfere in invasive techniques