Objective: To identify brain regions generating tics in patients with Tourette syndrome using sleep as a baseline. Methods: We used [O-15]H2O PET to study nine patients with Tourette syndrome and nine matched control subjects. For patients, conditions included tic release states and sleep stage 2; and for control subjects, rest states and sleep stage 2. Results: Our study showed robust activation of cerebellum, insula, thalamus, and putamen during tic release. Conclusion: The network of structures involved in tics includes the activated regions and motor cortex. The prominent involvement of cerebellum and insula suggest their involvement in tic initiation and execution.