Background: The anatomical variations of the brachial plexus in formation and distribution are well documented. Objective: The aim of this study was to describe the variations in the formation and branching pattern of posterior cord of brachial plexus. Material & Methods: Twenty one male adult cadavers were used in this study. The neck, antero-lateral thorax and delto-scapular areas were carefully dissected to expose the origin of the brachial plexus branches from the cervico-axillary roots to their terminations. Variations of trunks, divisions and cords of the brachial plexus were also explored, as well as the pattern of posterior cord formation and the origin of its branches. Each finding was ordered, photographed, and registered. Results: The classic formation of the posterior cord from the posterior divisions of the brachial plexus trunks was seen in 88% of the limbs. However, different unusual patterns of posterior cord formation were seen in the other 12% of the limbs. The variations in the posterior cord formation and its branching pattern were equally distributed on both sides of the limbs and they were not noticed bilaterally in any cadaver. The classic (usual) branching pattern of the posterior cord was seen in 57.1% of upper subscapular, 71.4% of lower subscapular, 71.4% of thoracodorsal nerves as well as in 42.9% of long thoracic nerve and 85.7% of suprascapular nerve. However, in 42.9% of upper subscapular, 28.6% of lower subscapular, 28.6% of thoracodorsal, 57.1% of long thoracic and 14.3% of suprascapular nerves showed unusual origin. The middle (accessory) subscapular nerve was seen only in 42.9% of the limbs. In 23.8% of these limbs, the posterior cord was the origin of this nerve. However, the posterior division of the upper trunk gave its origin in 7.1% of the limbs. Moreover, the posterior division of the upper trunk was the common unusual origin of the upper subscapular nerve (38.1%) and the suprascapular nerve (9.5%) while; the axillary nerve was the common unusual origin of the lower subscapular nerve (21.4%). The radial nerve was the common unusual origin of thoracodorsal nerve (16.7%). However, the late union of long thoracic nerve roots (C5, 6, 7) was seen in 33.3% of the limbs. Moreover, in 24.8% of the limbs, the long thoracic nerve was formed from two roots only (absence of C7 or C5). Indeed, the subscapular and suprascapular arteries perforated the posterior cord in one limb each. A connection between radial nerve and medial cord was seen in two limbs (4.8%) only. Conclusion: Knowledge of brachial plexus anatomical variations is important for clinicians in the fields of surgery, neurosurgery, orthopaedic surgery, vascular surgery, neurology, anasethiology and radiology, especially during performing surgical exploration or anaesthesiological procedures in axillary and neck regions.