The purpose of this study is to determine the areas of the brain responsible for tics in patients with Tourette's syndrome and chronic motor tic disorder using [15O]H2O. Previous neuroimaging studies have looked at brain activity during tics using functional magnetic resonance imaging (fMRI), and positron emission tomography (PET), but a major drawback of these studies lay in the difficulty distinguishing between the activity in the brain responsible for tic generation versus activity in motor-related structures due to tic movements. We plan to overcome this difficulty in our paradigm using two rest conditions without any movement. One is a state when patients suppress their tics and the second is sleep state, when tics usually cease or are at least very infrequent. 23 adult patients with a DSM-IV-TR (American Psychiatric Association 2000) diagnosis of a tic disorder and frequent tics will be studied. These two rest states will be compared with a condition where tics are allowed to occur spontaneously. The differential activation of brain areas between these three conditions should help to elucidate/define the regions of the brain responsible for generation of tics.