OBJECTIVE To evaluate the efficacy and safety of guanfacine in children with attention-deficit hyperactivity disorder (ADHD) and tic disorders. METHODS Twenty-five medication-free subjects (23 males and 2 females), aged 7-16 (mean = 10.6 +/- 2.0) years participated in an 8-week open-label guanfacine study. Subjects were recruited from a specialty clinic for children with tic disorders over a four-year period. Eligibility criteria included presence of ADHD (any type), a tic disorder (any type), and being medication free for two weeks. Outcome measures included the Hyperactivity Index of the Conners Parent Questionnaire, the teacher-rated ADHD Rating Scale, and the Yale Global Tic Severity Scale (YGTSS). RESULTS All subjects met criteria for ADHD (combined type N = 22; predominantly inattentive type N = 3) and a tic disorder (Tourette's Disorder N = 20; chronic motor tic disorder N = 5). At an average dose of 2.0 +/- 0.6 mg/ day, guanfacine was associated with mean improvement of 27% on the Hyperactivity Index (N = 25; t = 4.61; p < 0.001), 32% on the total score of the teacher-rated ADHD Scale (N = 19; t = 5.27; p < 0.001), and 39% on the total tic severity scale (N = 19; t = 4.17; p < 0.001). Mild and statistically insignificant decreases in blood pressure and pulse were observed in the sample as a whole. Five subjects had endpoint systolic blood pressure below 1 SD from their age and gender norms. CONCLUSIONS Results of this open-label study add to the growing data base on the safety and efficacy of guanfacine in children with ADHD and tic disorders.