Harlequin syndrome is a rare autonomic disorder with at least 83 reported cases in literature, 6% of which are congenital. When the fibers responsible for sudomotor and vasomotor supply to the face at the T2-T3 level are unilaterally blocked, it leads to hemifacial discoloration. This results in one-half of the face appearing flushed and hyperemic, sharply contrasting with the pale appearance of the other half. The cause of this syndrome is unknown
however, it appears to involve an autonomic nervous system dysfunction. It can be caused by an injury, compression, or blockade of sympathetic fibers along the pathway. The present study was a case of a metastatic osteosarcoma patient with a history of video-assisted thoracic surgery pleurectomy that presented in Attikon University Hospital (Athens, Greece) with worsening dyspnea and right-sided facial flushing.