During previous dissections to investigate the incidence of the third head of the biceps brachii in neonate cadavers an accessory coracobrachialis muscle was unilaterally found in a neonate male cadaver. This muscle originated from the coracoid process and the capsule of the shoulder joint. It was inserted into the antebrachial fascia and the medial epicondyle of the humerus. The coracobrachialis muscle is used as a transposition flap in deformities of infraclavicular and axillary areas and in postmastectomy reconstruction. It is also a guide to the axillary artery during surgery and anesthesia. This additional muscle may cause musculocutaneous or high median nerve paralysis. We were unable to find any similar case in the published literature. The anatomic variations of the coracobrachialis muscle may cause confusion during surgery or evaluation of CT and MRI scans.