How should sleep-related rhythmic movements in children be assessed and treated? Rhythmic movement disorder (RMD) represents an unusual variety of childhood parasomnia characterized by repetitive motion of the head, trunk, or extremities, which usually occurs during the transition from wakefulness to sleep or arises during sustained sleep. Although the condition most often affects infants and toddlers in a transient and self-limited fashion, the condition occasionally persists in a problematic fashion, which may nevertheless be amenable to treatment. Since RMD may occasionally cause injury or resemble nocturnal seizure, prompt recognition, and appropriate management on the part of the clinician is essential. This article will examine the spectrum of RMD in children, including their common clinical manifestations; data regarding their epidemiology and natural history; the role of polysomnography, electroencephalography; and other diagnostic testing. Potential causes of the condition and available methods of treatment are also examined.