Parasomnias are frequent. They usually represent either the exaggeration of a physiological phenomenon (e.g. sleep starts) or a non-disturbing, idiopathic and usually benign sleep disorder (e.g. sleep talking and bruxism), which need only counseling and improvement of sleep hygiene. However, occasionally parasomnias are of clinical relevance. They can cause insomnia or hypersomnia (e.g. 'myoclonus nocturnus'), psychosocial stress (e.g. sleep-related enuresis and sleep walking) and injuries to oneself and others (e.g. REM-parasomnia). Finally, they can be symptomatic of neurological and medical disorders (e.g. sleep paralysis and 'myoclonus nocturnus'). In these cases special investigations including video-polysomnography can establish a correct diagnosis and allow a specific treatment.