Disorders of impulse control are frequently associated with adult psychiatric diagnoses (e.g., borderline personality disorder, kleptomania, explosive disorder, pyromania) as well as disorders with a typical onset in childhood (e.g., Tourette's syndrome, tic disorders, attention-deficit hyperactivity disorder). Behavioral and personality changes are also commonly found in adult neurological diseases. In fact, an inability to restrain one's impulses and control behavior may be the initial symptom or primary complaint noted by concerned family members or by neurologists when examining a patient for potential central nervous system (CNS) dysfunction. In this chapter we focus on the etiology and clinical presentation of impulsiveness associated with adult neurobehavioral disorders.Pathological impulsivity can be conceptualized as a failure to regulate, monitor, or control behavior and emotional expression. Because