Tourette's disorder (TD), which is characterized by multiple waxing and waning motor tics and one or more vocal tics, is known to be associated with abnormalities in the dopaminergic system. To testify our hypothesis that risperidone would improve tic symptoms of TD patients through the change of the dopaminergic system, we measured the dopamine transporter (DAT) densities between drug-naive children with TD and normal children, and investigated the DAT density before and after treatment with risperidone in drug-naive children with TD, using iodine-123 labelled N-(3-iodopropen-2-yl)-2β-carbomethoxy -3beta-(4-chlorophenyl)tropane ([123I]IPT) single photon emission computed tomography (SPECT). MATERIALS and METHODS: [123I]IPT SPECT imaging and Yale Global Tic Severity Scale-Korean version (YGTSS-K) for assessing the tic symptom severity were carried out before and after treatment with risperidone for 8 weeks in nine drug-naive children with TD. Eleven normal children also underwent SPECT imaging 2 hours after an intravenous administration of [123I]IPT. RESULTS: Drug-naive children with TD had a significantly greater increase in the specific/nonspecific DAT binding ratio of both basal ganglia compared with the normal children. However, no significant difference in the specific/nonspecific DAT binding ratio of the basal ganglia before and after treatment with risperidone in children with TD was found, although tic symptoms were significantly improved with risperidone. CONCLUSION: These findings suggest that DAT densities are directly associated with the pathophysiology of TD, however, that the effect of risperidone on tic symptoms in children with TD is not attributed to the change of dopaminergic system.