About 40% of adults are habitual snorers. 2% of women and 4% of men between 30 and 60 years of age present additional sleep disordered breathing. There is a continuous spectrum from simple to disease-causing snoring ranging from merely disturbing noises to pharyngeal obstructions and breathing pauses. Repetitive episodes of upper airway obstructions lead to frequent arousals from sleep. Sleep fragmentation is responsible for non-refreshing sleep and subsequent excessive daytime sleepiness resulting in reduced performance at work, social problems and a higher risk for accidents. Furthermore there is a correlation between arousals and cardiovascular abnormalities. Anatomic narrowing of the upper airway or hypotonia of the orpharyngeal dilator muscles favour collapse of the oropharyngeal walls. Obstructive sleep apnea syndrome is characterized by repetitive oxyhemoglobin desaturations during sleep recorded by pulseoximetry. Polygraphy quantifies the average number of apneas and hypopneas which occur during one hour of sleep (apnea-hypopnea index = AHI). In upper airway resistance syndrome (= UARS), upper airway resistance is increased, but pharyngeal obstruction is not complete. Saturation doesn't decrease significantly, but arousals with consecutive sleep disruption still occur. Polysomnography is a comprehensive study including EEG-, EOG- and EMG-recordings. Sleep stages and events can be scored to evaluate sleep architecture, sleep efficiency and sleep fragmentation.