OBJECTIVE: Adverse drug events (ADEs) are a common complication of medical care, but few pediatric data are available describing the frequency or epidemiology of these events. We estimated the national incidence of pediatric ADEs requiring medical treatment, described the pediatric population seeking care for ADEs, and characterized the events in terms of patient symptoms and medications implicated. METHODS: Data were obtained from the National Center for Health Statistics, which collects information on patient visits to outpatient clinics and emergency departments throughout the United States. We analyzed data for children 0 to 18 years of age seeking medical treatment for an ADE between 1995 and 2005. RESULTS: The mean annual number of ADE-related visits was 585922 (95% confidence interval [CI]: 503687-668156) of which 78% occurred in outpatient clinics and 12% occurred in emergency departments. Children 0 to 4 years of age had the highest incidence of ADE-related visits, accounting for 43.2% (95% CI: 35.6%-51.2%) of visits. The most common symptom manifestations were dermatologic conditions (45.4% [95% CI: 36.9%-54.1%]) and gastrointestinal symptoms (16.5% [95% CI: 11.1%-23.8%]). The medication classes most frequently implicated in an ADE were antimicrobial agents (27.5% [95% CI: 21.5%-34.5%]), central nervous system agents (6.5% [95% CI: 4.0%-10.5%]), and hormones (6.1% [95% CI: 3.1%-11.6%]). While ADEs related to antimicrobial agents were most common among children 0 to 4 years old and decreased in frequency among older children, ADEs resulting from central nervous system agents and hormones increased in frequency among children 5 to 11 and 12 to 18 years old. CONCLUSIONS: ADEs result in a substantial number of health care visits, particularly in outpatient clinics. The incidence of ADEs and medications implicated vary by age, indicating that age-specific approaches for monitoring and preventing ADEs may be most effective.