The present article comprehensively reviews the thoracic outlet syndrome (TOS), its etiology and assessment, with reference to the usual conservative treatment and surgical therapy, highlighting new definitions and reporting obsolete tests. The syndrome affects about 8% of the population, with higher prevalence in females, and rarely affects the children. Conservative, non-surgical treatment produces good results, and it becomes important to know which specific areas need to be treated. Currently, there is no rehabilitation scheme, either osteopathic or chiropractic, considered as a valid tool for a precise localization of the pathologic condition, probably due to the lack of a manual assessment process to evaluate bones and muscular components of the thoracic outlet. In this situation, the manual treatment performed is usually generic. The present article proposes a manual evaluation that can be used to identify the anatomical area which needs to be treated. This hypothesis of assessment should be carried out after the clinician has ruled out the necessity of surgery with instrumental examinations.