Zonisamide is a broad-spectrum antiepilepsy drug approved in the United States for the adjunctive treatment of partial seizures in adults with epilepsy. Studies in Japan have established zonisamide as effective and safe for use in children, but there is limited information from the United States concerning its use in pediatric patients. This chart-review study was conducted to evaluate the efficacy, safety, and appropriate dosage of zonisamide for treating seizures in pediatric and adolescent patients. Charts of 50 pediatric patients (mean age 9.1 years, range 9 months to 20 years) who received zonisamide were evaluated for demographic characteristics, seizure types, dosage (mean = 15.8 mg/kg/day), response, concurrent medications, and adverse events. After treatment, 8 patients were seizure-free, and 11 others had > or =50% improvement in seizure control, including 11 of the 28 patients for whom treatment with six or more antiepileptic drugs was insufficient. Thirty-one patients experienced at least one adverse event while receiving zonisamide, and 14 discontinued as a result.