Upper Airway Resistance Syndrome (UARS) was initially used to describe a group of patients who were sleepy but did not meet the diagnostic criteria of obstructive sleep apnea syndrome (OSAS). Since the original description, controversy and ambiguity of this disorder have lead to limited amounts of adequate data and studies. The incidence, prevalence, natural history, and morbidity of this disorder are not well known, and the diagnosis of UARS remains a controversial issue. Advances in technology have lead to measurement of sensitive polysomnographic variables that may aid in effectively identifying this disorder, distinguishing it from OSAS. Recognition of patients with UARS is important because although these patients are symptomatic, they may not present with the same symptoms as patients with OSAS. Treatment options are available that may benefit patients with UARS. This article reviews the pathophysiology, diagnosis, clinical picture and management of UARS.