The incidence of adverse drug events (ADEs) among children has been well characterized in hospital inpatients, but less studied in the outpatient setting. Conducted at six pediatric outpatient practices, this AHRQ-funded prospective cohort study evaluated the frequency of medication errors via chart review, review of prescriptions, and patient surveys. The overall rate of preventable ADEs was similar to a prior outpatient study, but nearly three-quarters of events were attributable to errors in administering drugs by the parents. Parents also did not consistently inform clinicians of ameliorable ADEs when they occurred, leading the authors to conclude that communication between clinicians and parents around the issue of medication side effects must be improved.