Complex motor stereotypies are rhythmic, repetitive, fixed, and non-goal directed movements (e.g., bilateral flapping/waving movements of the hands/arms). Movements typically begin in early childhood and can occur in otherwise normally developing ("primary") or autistic ("secondary") children. Stereotypies persist, occur multiple times a day, have prolonged durations, can be socially stigmatizing, and may lead to bullying and isolation. Prior behavioral treatment studies have focused on older children (ages 6-12) and report modest reductions in stereotypy (i.e., between 14% and 33%). The current study involves the functional assessment and treatment of five children with Primary Complex Motor Stereotypy using a modified awareness training procedure, differential reinforcement of other behavior, and schedule thinning in a nonconcurrent multiple baseline design. Results suggest a 99% reduction of motor stereotypy from baseline across all participants.