Objective: To examine the safety and efficacy of immediate-release methylphenidate (MPH-IR) for the treatment of attention-deficit/hyperactivity disorder (ADHD) in children (ages 6-12 years) with Tourette's syndrome (96%) or chronic motor tic disorder (4%). Method: Two cohorts of prepubertal children (N = 71) received placebo and three doses of MPH (0.1, 0.3, and 0.5 mg/kg) twice daily for 2 weeks each, under double-blind conditions as part of their involvement in a long-term observation study (1989-2004). Treatment effects were assessed with an extensive battery of parent-, teacher-, child-, and physician-completed rating scales and laboratory tasks. Results: MPH-IR effectively suppressed ADHD, oppositional defiant disorder, and peer aggression behaviors. There was no evidence that MPH-IR altered the overall severity of tic disorder or obsessive-compulsive disorder behaviors. Teacher ratings indicated that MPH-IR therapy decreased tic frequency and severity. Conclusions: MPH-IR appears to be a safe and effective short-term treatment for ADHD in the majority of children with chronic tic disorder; nevertheless, the possibility of tic exacerbation in susceptible individuals warrants careful monitoring of all patients. (Contains 4 tables.)