The Harlequin syndrome, first described by Lance et al.1 in 1988, represents an uncommon disorder of the sympathetic nervous system. It is characterized by unilateral diminished sweating and heat- or exercised-induced facial flushing. We present the case of one patient with this remarkable syndrome, including a review of the literature. A 43-year-old woman presented to our clinic with a peculiar pattern of facial flushing. She has been experiencing flushing and sweating on the left side of her face after physical exercise or after taking a hot bath (Fig. 1). The symptoms started about 2 years ago, after she had undergone an endoscopic surgery for the removal of a solitary pulmonary nodule. She has no other medical history besides chronic pancreatitis. She has never been treated for her symptoms before visiting our clinic. On examination at rest, no asymmetric facial flushing or sweating was noted. Neurological examination was normal, and signs of ptosis or miosis were absent. Laboratory tests, including complete blood count, erythrocyte sedimentation rate, glucose, sodium, potassium, and creatinine, revealed no abnormality. As the symptom had appeared only after the endoscopic surgery, we suspected that there might have been an accidental damage to the sympathetic nerve innervating the right facial area during the surgery. The patient was reassured of the benign nature of her complaints and was asked to avoid any aggravating factors. Most cases of Harlequin syndrome are primary in nature. This syndrome is most common in women, and social embarrassment is the main problem of affected persons. In about one-sixth of patients with Harlequin syndrome, the disorder is caused by an underlying disease or a structural lesion (i.e., secondary Harlequin syndrome). The iatrogenic type of Harlequin syndrome, like our case, is recently being reported with a higher frequency. Ten such cases have been reported: one occurring after internal jugular vein catheterization, five after paravertebral thoracic anesthetic blocks, three after surgical resection of a neck mass, and one after thoracic sympathectomy. Physicians should focus on taking the patient's medical history for related factors such as a previous malignancy, as well as recent surgery or anesthesia-related problems. Clinical and neurological examinations are also required, and imaging techniques such as computed tomography or magnetic resonance imaging of the brain, spinal cord, and the carotid arteries and the lung apex should be performed to exclude the presence of a structural lesion. Usually, a patient with a primary or iatrogenic Harlequin syndrome does not need any treatment. If the symptoms are not acceptable, a contralateral sympathectomy may be considered2. Recently, a novel approach to the management of Harlequin syndrome, by using repeated stellate ganglion blocks, was proposed as a less invasive alternative treatment3. To our knowledge, a clinical presentation of Harlequin syndrome has not been previously reported in the Korean dermatological literature. We hope that this report would make dermatologists properly aware of this rare syndrome.