Abstract A large body of evidence suggests that abnormal dopaminergic activity is present in Gilles de la Tourette Syndrome (GTS). To invesligate whether dopamine dysregulation involving the D 2/D 3 receptor occurs in GTS, we performed single slice dynamic single pholon emission computed tomography (SPECT) with 123iodo-6-methoxybenzamide ( 123I-IBZM) in 15 GTS patients (eight unmedicated) and six healthy volunteers. After intravenous administraiion of 5 mCi (185 MBq) of 123I-IBZM, dynamic SPECT (5 minutes per slice) studies were performed at the level of the basal ganglia for 55 minutes. The mean activity per pixel in the basal ganglia was compared with the mean activily per pixel in the visual cortex. Unmedicated GTS patients showed no differences from control subjects. However, GTS patients taking D 2 blocking medications had significantly decreased 123IIBZM binding compared with control subjects in both the right and left basal ganglia. Thus, D 2/ D 3 receplor availability, as measured by 123I-IBZM SPECT, is nol abnormal in GTS.