Stereotypic movement disorder (SMD) is a motor disorder with onset in childhood involving restrictive and/or repetitive, nonfunctional motor behavior (e.g., hand waving or head banging), that markedly interferes with normal activities or results in bodily injury. To be classified as SMD, the behavior in question must not be due to the direct effects of a substance, autism, or another medical condition. The cause of this disorder is not known.