Prior research has found that adverse drug events are a common source of emergency department (ED) visits and hospital admissions in adults. This prospective observational study involved more than 2000 pediatric patients presenting to an ED at a tertiary academic medical center in Canada. Medications were directly related to the presenting chief complaint in 8% of patients, with two-thirds of these deemed preventable. The vast majority of medication-related visits were classified as causing moderate harm, but approximately 5% of cases were severe. Children with a medication-related ED visit were much more likely to be admitted to the hospital and to have a longer length of stay than children presenting to the ED with other problems. The results of this study add to a prior systematic review by the same research group, which also found that a significant proportion of adverse drug events in pediatric patients presenting to the ED were likely avoidable.