OBJECTIVES: Previous studies in patients with Tourette's disorder suggested presynaptic dopaminergic dysfunction, demonstrating increased dopamine densities. In present study, we investigated dopamine transporter densities using I-123N-(3-iodopropen-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl)tropane(I-123-IPT)-SPECT in drug-naive children with Tourette's disorder and postulated that dopamine transporter density reflected dopamine concentrations. METHODS: Eight drug-naive children with Tourette's disorder and six normal children were included in the with the brain SPECT 2 hours after an intravenous administration of I-123-IPT. Obtained SPECT data were reconstructed for the assessment of specific/nonspecific dopamine transporter binding ratio of basal ganglia and were evaluated both quantitatively and qualitatively. We investigated correlation between total tic severity of children with Tourette's disorder assessed with YGTSS and specific/nonspecific binding ratio of basal ganglia. RESULTS: Drug-naive children with Tourette's disorder had a significantly greater increase of speciffic/nonspecific dopamine transporter binding ratio of left basal ganglia than normal children. However, no significant differences in specific/nonspecific dopamine transporter binding ratio of right basal ganglia were found between children with Tourette's disorder and normal children. Also, we found no significant correlation between total tic severity of children with Tourette's disorder and specific/ nonspecific binding ratio of basal ganglia. CONCLUSION: These findings support the hypothesis of dopamine dysregulation in presynaptic dopamine function of the basal ganglia in the pathophysiology of Tourette's disorder.