10.22376/ijpbs.2019.10.1.p1-12 Volume 9 Issue 1 2018 (January-March) The sternocleidomastoid muscle is important anatomically and clinically because of its relationship with many neurovascular structures in the neck and is one of the most complex muscles of the body. A wide mention of supernumerary and accessory musculature has been made in the literature. In majority of cases, accessory head of sternocleidomastoid are asymptomatic and usually incidental findings at surgery or imaging. The aim of this study was to determine the morphologic features, the prevalence of additional head of the sternocleidomastoid muscle and describe bilateral muscular anatomical variations in the neck region. A total of 18 cadavers of both sexes with different age group were used for the study. Head and neck region (36 sides) of the cadavers were carefully dissected in the Morphology Laboratory at the University of Pamplona. The morphological variations in the number of heads (six, four and three) of origin of the sternocleidomastoid muscle were observed in 6 out the 36 sides of the neck (16.6%). In three male subjects it was found in right and left neck, bilaterally. The remaining 30 sides of the neck (83.4%) showed the normal origin, insertion of the sternocleidomastoid and the course and branching patterns of the spinal accessory nerve and arterial patterns was normal. These variations must be kept in mind while approaching the region to avoid complications as the classical anatomical landmarks might be misinterpreted and confused. It might cause difficulties in the surgery in that region. It may also interfere in invasive techniques. HUMBERTO FERREIRA-ARQUEZ* Anatomical variation, sternocleidomastoid muscle, clavicular head, sternal head 249-256