Movement disorders are a group of diseases and syndromes affecting the ability to produce and control movement.

Though it seems simple and effortless, normal movement in fact requires an astonishingly complex system of control. Disruption of any portion of this system can cause a person to produce movements that are too weak, too forceful, too uncoordinated, or too poorly controlled for the task at hand. Unwanted movements may occur at rest. Intentional movement may become impossible. Such conditions are called movement disorders.

Abnormal movements themselves are symptoms of underlying disorders. In some cases, the abnormal movements are the only symptoms. Disorders causing abnormal movements include:

• Parkinson's disease
• Parkinsonism caused by drugs or poisons
• Parkinson-plus syndromes (progressive supranuclear palsy, multiple system atrophy, and cortical-basal ganglioric degeneration)
• Huntington's disease
• Wilson's disease
• Inherited ataxias (Friedreich's ataxia, Machado-Joseph disease, and spinocerebellar ataxias)
• Tourette syndrome and other tic disorders
• Essential tremor...