Clonidine is an alpha-adrenergic agonist which may alleviate emerging symptoms in Tourette syndrome, an observation that has fueled speculation regarding involvement of stress-sensitive central noradrenergic systems in this disorder. We conducted a retrospective study of 53 juvenile patients with Tourette syndrome to assess predictors of short-term behavioral and tic response to oral clonidine and to examine the relationship, if any, among pretreatment blood pressure, tic severity, and clonidine response. When adverse effects were considered, older subjects experienced a better therapeutic response to clonidine, independent of dose. Improvement in symptoms of attention-deficit hyperactivity disorder was associated with a longer duration of vocal tics before treatment. Baseline sitting diastolic blood pressure was directly correlated with measures of tic severity but not with tic response to clonidine. The findings (1) provide indirect support for involvement of central noradrenergic systems in tic expression; (2) suggest that emergence of a tic-related neurophysiologic dysfunction may be necessary for optimal behavioral response to clonidine in Tourette syndrome; and (3) provide broad guidelines for the clinician considering clonidine therapy for pediatric patients with Tourette syndrome, particularly those with comorbid attention-deficit hyperactivity disorder.