Pathophysiology of the obstructive sleep apnea syndrome shows three components: intra and peripharyngeal obstacles, excessive pharyngeal wall compliance and upper airway dilator muscle dysfunction. The intent of this paper is to provide an overview of the anatomy, histology, physiology and pathophysiology of the upper airway dilator muscles based on previously published articles. The upper airway dilator muscles can be separated in three different systems, main and accessory dilators, local and regional. They act in synergy. Their contraction occurs at the beginning of inspiration, thus maintaining opened the pharyngeal lumen through inspiration. Their action is modulated by several chemo or physical stimuli. In some apneic patients, these muscles demonstrate a dysfunction: hyperactivity during wakefulness, electromyogram wave amplitude reduced, delayed contraction during sleep and abnormal response to stimuli. This dysfunction might be due to neuromuscular histological abnormalities, a "fatigue" phenomenon or a central nervous command abnormality. Current explorations underlining an upper airway dilator muscle dysfunction will enable practitioners to decide which treatment is best and understand therapeutical failures; it will also help develop new therapeutical techniques such as functional electrical stimulation of the hypoglossal nerve/upper airway dilator muscles.