As its name implies, Stereotypic Movement Disorder describes a disorder — mainly in children — that causes a sufferer to repeatedly perform the same motion or movement, uncontrollably. This is much different than an Obsessive-Compulsive Disorder, which can manifest itself as a repeated ritual such as washing hands dozens of times per day. To qualify as an SMD, a movement must be a non-functional motor behavior, repeated to the point that it either interferes with normal activities or results in self injury.
Although Stereotypic Movement Disorder is closely associated with mental retardation and developmental problems in children, the obsessive movements outlined above can slowly manifest in normal children and adults in order to cope with psychological trauma.
SMD is often associated with Tourette syndrome (compulsively swearing), though the two originate from different psychological imbalances. Also similar to Stereotypic Movement Disorder is the good old “tic”. However, a facial tic or eye-blinking tic doesn’t necessarily qualify either as a full-blown SMD, since perfectly healthy people exhibit tics that don’t unduly interfere with their normal activities.