This study examined response to methylphenidate in children with attention-deficit/hyperactivity disorder (ADHD) and chronic multiple tic disorder. The primary goal was to determine if children with anxiety or depression symptoms showed a less favorable response to treatment. Subjects were 38 prepubertal children who participated in an 8-week, double-blind, placebo-controlled, methylphenidate crossover evaluation. Treatment effects were assessed with direct observations of child behavior in public school and clinic settings; rating scales completed by parents, teachers, and clinicians; and laboratory analogue tasks. There was little evidence (group data) that children with anxiety or depression symptoms responded in a clinically different manner to methylphenidate than youngsters who did not exhibit these symptoms, particularly in school observations of the core features of ADHD. Seeming differences between children with and without comorbid anxiety or depression symptoms and drug response are likely explained by differences in pretreatment levels of negativistic behaviors (i.e., symptoms of oppositional defiant disorder or conduct disorder). Methylphenidate appears to be effective for the management of ADHD behaviors in children with mild to moderate anxiety or depression symptoms; nevertheless, much research remains to be performed in this area.