REM sleep behavior disorder (RBD) is one of the most important factors predicting Parkinson's disease. Symptoms constitute vivid dreams typically characterized by ominous contents and associated muscular activity. Specific signs include the preservation of muscle tone during REM sleep as detected in polysomnography, and behavior associated with dreaming as demonstrated by video monitoring. Injury risk is increased during the attacks. Melatonin or clonazepam can be used as therapy. The disorder belongs to the entity of synucleinopathies.