An account is given of Gilles de la Tourette syndrome in three patients, two of whom were successfully treated by behaviour therapy. Aspects of these cases and of others reported in the literature cast some doubt on whether there is anything to be gained by considering such allegedly rare cases as separate from other cases of verbal or motor tic, and it is shown that behaviour therapy is perhaps the most efficient, lasting and brief treatment available to such patients. Some of the difficulties of its administration are discussed and illustrated in both successfully and unsuccessfully treated cases, and finally some enlargement of contemporary theory of the condition's causative mechanism is offered in terms of a disturbance of or imbalance between cortical and autonomic arousal mechanism. The symptom occurs because a motor tic is originally learned to be a reducer of high autonomic drive and at the same time an activator of cortical arousal mechanisms, which themselves because of the constitutionally extraverted nature of the subjects produce cortical inhibition levels by satiation far above a level which allows of adequate motor and verbal control. Treatment that is to be successful, then, must be aimed at reducing autonomic arousal and eliminating these satiation effects by cutting down the spontaneous incidence of the tic by deliberate practice of it.