The literature and experience in the treatment of over 800 patients with tics and Tourette syndrome is critically assessed to provide a guide for treatment. Medications are classified and discussed according to their neurochemical actions to provide heuristic insights about the etiology of tics and Tourette syndrome. The effectiveness of haloperidol suggests excessive presynaptic levels or postsynaptic sensitivity to normal levels of dopamine. However, the clinical effects of other drugs, with known or presumed actions on neurotransmitters, and studies of specific neurotransmitters and their enzymes, do not support any of the hypotheses about abnormal levels of dopamine or other catecholarmines. The evidence supporting various neuroanatomic or neurochemical theories is inconclusive.