Six generations of a family with paroxysmal choreoathetosis of the Mount and Reback type were studied. Neurological investigation and follow-up of the symptoms were possible for four generations, in which 15 members suffered from the disease. The attacks could be provoked by alcohol and intensified by caffeine or emotional excitement. Phenytoin, primidone and carbamazepine had no therapeutic effect. Treatment with L-dopa could provoke the choreoathetosis. Haloperidol was the most effective treatment and valproic acid was also able to reduce drastically the frequency and intensity of the attacks. Three patients with sporadic kinesiogenic, paroxysmal choreoathetosis were also studied, whose choreoathetosis was induced by movement. Treatment with carbamazepine or phenytoin was effective, but haloperidol increased the severity of the choreoathetoid attacks.