Abnormal movements or postures often present a diagnostic and therapeutic challenge to the psychiatrist or neurologist. The authors review pertinent anatomy and physiology of disorders of the extrapyramidal system, suggest aspects of the clinical history and examination particularly important for diagnosis, and describe a range of abnormal movements. They review several syndromes in which abnormalities of behavior and movement may occur together, including Huntington's chorea, Wilson's disease, Parkinson's disease, and tardive dyskinesia.