Rapid eye movement (REM) sleep behavior disorder is characterized by dream enactment during REM sleep. Due to different treatment requirements, it is important to distinguish REM sleep behavior disorder from other causes of nocturnal restlessness, including sleep apnea, non-REM parasomnia and sleep-related hypermotor epilepsy. In addition, a diagnosis of isolated REM sleep behavior disorder is impactful, because it carries a greatly increased risk for the later development of Parkinson's disease and related synucleinopathies. In this clinical lesson we describe three patients with abnormal nocturnal movements and vocalizations. The history can provide important clues towards the diagnosis, but a video-polysomnography is required before REM sleep behavior disorder can be diagnosed.