Brachial plexus compression in neurogenic thoracic outlet syndrome (TOS) may occur either at the level of the supraclavicular scalene triangle and/or the infraclavicular subcoracoid space. As highlighted elsewhere by Sanders (Chap. 15), it has only recently been recognized that nerve compression at the level of the pectoralis minor muscle tendon can make a substantial contribution to symptoms in neurogenic TOS, and that in many cases nerve compression at this level may dominate over that occurring at the level of the scalene triangle. Untreated pectoralis minor compression of the brachial plexus may therefore represent an important factor in persistent or recurrent symptoms following operations for neurogenic TOS, and undoubtedly explains a proportion of surgical failures in previous clinical series. Moreover, it is now apparent that a significant number of patients may have a clinical diagnosis of neurogenic TOS represented by isolated brachial plexus compression at the level of the pectoralis minor muscle, for whom isolated pectoralis minor tenotomy may provide a min- imally-invasive surgical option associated with rapid postoperative recovery and a high likelihood of clinical success. Recognition and treatment of this condition has therefore been an important step in our evolving understanding of neurogenic TOS.