Introduction. Harlequin syndrome is a very rare neurological condition characterized by redness and excessive sweating of one half of the face in response to exercise and emotions. In most cases this disorder is not life-threatening.

Objective. To present diagnostic difficulties of Harlequin syndrome in dermatological practice.

Case report. We present a case of a 30-year-old man with redness and excessive sweating of the right half of the face as a result of exercise that was observed during the diagnosis of chronic urticaria at the Department of Dermatology. The patient was examined ophthalmologically and neurologically, had a CT scan of the head, and the Minor test performed. Idiopathic Harlequin syndrome was diagnosed based on case history and workup results.

Conclusions. Harlequin syndrome occurs most often in the form of an idiopathic condition, but neurologic and ophthalmologic assessment should be performed since some diseases, such as brainstem infarction and schwannoma of the upper chest, may initially appear as Harlequin syndrome.