Biological and psychosocial features influence the outcome of haloperidol treatment of multiple tic syndrome. Responders to haloperidol who have a family history of tics may suffer from a genetic and metabolic disorder, whereas nonresponders, who are inclined to perinatal abnormalities and have a later onset of tics, have an acquired disorder. Behavioral disturbances and psychosocial adaptation may influence or be influenced by drug usage. The hypothesis of uric acid metabolic abnormality was not supported but dopaminergic and/or γ-hydroxybutyrate neural systems may be implicated.