Rhythmic movement disorder (RMD), also known as stereotypic movement disorder (SMD; American Psychiatric Association, 1994), jactatio captis nocturna and rythmie de sommeil, refers to a group of stereotypical, rhythmic, repetitive movements or vocalizations. RMD is diagnosed if it occurs in children particularly preschool-age children during drowsy or sleep periods or during the sleep-wake period of the sleep cycle, unlike other types of movement disorders, including SMD.