The objectives of the present study were to examine clonidine use before and after initiation of atomoxetine in a cohort of children with attention deficit/hyperactivity disorder (ADHD). For this purpose, medical and pharmaceutical claims data for patients from 75 managed health care plans across the United States were extracted to identify a cohort of patients aged 18 years and younger at the time of a first atomoxetine prescription. Clonidine users were characterized on the basis of demographics, comorbid conditions, medication use and provider types, and prescribing patterns before and after the index atomoxetine prescription assessed. Subgroups of patients switching from clonidine to atomoxetine were examined and predictors of ongoing or new clonidine use were assessed. Of patients filling a first prescription for atomoxetine, 9.6% received a prescription for clonidine at some time and 4.3% within the previous 2 months. Children identified with a hyperactive component to their ADHD, those with more complex diagnostic histories, and those with tics and sleep disorders were particularly likely to receive clonidine. More than a third of patients (36.5%) with recent clonidine use subsequently discontinued use, with the pattern of clonidine use before and after atomoxetine use being highly dependent upon the pattern of stimulant prescription. Atomoxetine, in some cases, seems to have replaced clonidine in the treatment of patients with ADHD complicated with comorbid psychiatric disorders. In others, atomoxetine has replaced both stimulant and clonidine in patients previously requiring this combination for the control of symptoms or for the management of stimulantrelated adverse effects.