Exposure to premonitory sensations and response prevention of tics (ER) has been shown to be a promising new treatment for Tourette's syndrome (TS). The present study tested the hypothesis that habituation to unpleasant premonitory sensations associated with the tic is an underlying mechanism of change in ER. Patients rated the severity of sensations and urges at 15-minute intervals during ten 2-hour ER sessions. Multilevel models using multiple time trend analyses showed significant reductions of the sensory severity ratings both within and between sessions. The decrease of these severity ratings was related to the frequency of tics exhibited during sessions, regardless of tic severity at baseline. These results support the hypothesis that habituation may be at least part of the underlying working mechanism of exposure in the treatment of tics in TS and that effective tic suppression during sessions is an important factor in this habituation process. (Contains 1 table and 3 figures.)