BACKGROUND: This study examined changes in attention-deficit hyperactivity (ADHD) behaviors and motor and vocal tics during long-term treatment with methylphenidate. METHODS: Thirty-four prepubertal children with ADHD and chronic multiple tic disorder (who had participated in an 8-week, double-blind, placebo-controlled methylphenidate evaluation) were evaluated at 6-month intervals for 2 years as part of a prospective, nonblind, follow-up study. Treatment effects were assessed using direct observations of child behavior in a simulated (clinic-based) classroom and behavior rating scales completed by parents and physician. Videotapes of the simulated classroom were scored by coders who were blind to treatment status. RESULTS: There was no evidence (group data) that motor tics or vocal tics changed in frequency or severity during maintenance therapy compared with diagnostic or initial double-blind placebo evaluations. Behavioral improvements demonstrated during the acute drug trial were maintained during follow-up. There was no evidence (group data) of clinically significant adverse drug effects on cardiovascular function or growth at the end of 2 years of treatment. CONCLUSIONS: Long-term treatment with methylphenidate seems to be safe and effective for the management of ADHD behaviors in many (but not necessarily all) children with mild to moderate tic disorder. Nevertheless, careful clinical monitoring is mandatory to rule out the possibility of drug-induced tic exacerbation in individual patients.