Sleep apnea syndrome (SAS) results from modification in the control of respiration and of upper airway caliber during sleep. Although there is some overlap between central (CSAS) and obstructive (OSAS) sleep apnea syndromes, each syndrome has specific pathological associations. The first part of this review concerns the pathophysiology of OSAS, including periodic breathing and upper airway collapse. In the second part, each specific etiology is examined, and the respective contribution of anatomic narrowing and neuromuscular dysfunction of the upper airway is mentioned. Our experience with about 375 patients with sleep-related breathing disorders is also reported, with regard to the specific etiologies of CSAS and OSAS.