The neuropathology of Tourette Syndrome (TS) is poorly characterized. This thesis provides the first quantitative stereologic immunohistochemical study of the basal ganglia in TS. TS is a childhood neuropsychiatric disorder characterized by motor and vocal tics. Previous imaging studies found alterations in caudate (Cd) and putamen (Pt) volumes. To investigate possible alterations in cell populations, postmortem basal ganglia tissue from individuals with TS and normal controls (NC) was analyzed using unbiased stereological techniques. A markedly higher (>160% of control) total neuron number and density was found in the internal segment of the globus pallidus (GPi) of TS (p<0.025). An increased number (>220% of control) and proportion of these GPi neurons were positive for the calcium-binding protein parvalbumin (PV) in the tissue from TS subjects (p<0.025). In contrast, a lower number (<60% of control) of neurons was observed in the external segment (GPe) (p<0.025). In addition, there was a lower density of PV-positive interneurons in both Cd (<50% of control) and Pt (<65% of control) (p>0.025). The imbalance in striatal and GPi inhibitory neuron distribution suggests that the functional dynamics of cortico-striato-thalamic circuitry are fundamentally altered in severe, persistent TS.