OSAS, a common cause of disrupted sleep and EDS, result from repetitive closure of the upper airway during sleep. It probably represents the most severe syndrome related to obstruction of the upper airway; less severe forms include UARS, a syndrome characterized by the need for increased effort to breath but no prominent apneas or hypopneas, and primary snoring. Initial clues to the presence of OSAS and related disorders are derived from the history and include loud snoring, EDS or insomnia, and witnessed apneas. Some patients, especially women, may complain mostly of tiredness or fatigue, and children may present with behavioral abnormalities. Obesity, a large neck circumference, and a crowded oropharynx are common on physical examination. Nonobese patients, in particular, often have retrognathia, a high-arched narrow palate, macroglossia, enlarged tonsils, temporomandibular joint abnormalities, or chronic nasal obstruction. The clinical suspicion of obstructed nocturnal breathing is confirmed by overnight polysomnography, and an MSLT may be used to assess sleepiness. Esophageal manometry during polysomnography facilitates diagnosis of UARS. Treatment most commonly consists of nasal CPAP or BPAP, although problems with compliance make surgical treatment preferable in some cases. Although UPPP eliminates sleep apnea only in a minority of patients, combining UPPP with maxillofacial procedures appears to improve outcomes. Other treatments such as the use of dental appliances or medications, weight loss, and positional therapy may be useful as adjunctive therapy for moderate to severe OSAS or as primary treatments for UARS or mild OSAS.