Although adverse drug events (ADEs) are relatively frequent in outpatient chemotherapy, little is known about ADE rates in pediatric cancer patients. This study examined data from the Medmarx voluntary reporting system to characterize the frequency and severity of such errors in pediatric patients. More than 300 errors were reported over the 5-year study period, approximately 15% of which resulted in clinical consequences (ie, the need for additional patient monitoring or therapeutic intervention). Errors in administering medications were the most common cause of adverse events, as noted in a previous study. The authors note that these errors probably would not be prevented by safety interventions such as computerized physician order entry.