A double-blind, dose-controlled study evaluated topiramate as monotherapy in 470 patients with newly diagnosed (< or = 3 months) epilepsy or epilepsy relapse in the absence of therapy. In addition to having at least 2 lifetime-unprovoked seizures, patients had 1 or 2 partial-onset seizures or generalized-onset tonic-clonic seizures during a 3-month retrospective baseline. The trial included a large cohort (N = 151, 32%) of children and adolescents 6 to 15 years of age. Eligible patients were randomized to treatment groups in which topiramate was titrated to target maintenance dosages of either 400 mg/day (n = 77) or 50 mg/day (n = 74). Patients were followed for at least 6 months. Based on Kaplan-Meier analyses, the primary efficacy endpoint of time to first seizure favored the higher topiramate dose in both the overall population and the cohort of children/adolescents. The probability that children/adolescents remaining in the study were seizure free at 6 months was 78% in the 50-mg target dose group and 90% with the higher dose. At 12 months, the probability of being seizure free was 62% and 85%, respectively. The incidence of treatment-limiting adverse events was 4% in the 50-mg target dose group and 14% in the group assigned to 400 mg as a target dose. The most common adverse events, excluding typical childhood illnesses, were headache, appetite decrease, weight loss, somnolence, dizziness, concentration/attention difficulty, and paresthesia. As shown in this subset analysis, topiramate is effective and well tolerated as monotherapy in children and adolescents.