This 24-week, multicenter, open-label trial was designed to evaluate the dosing, effectiveness, and safety of topiramate monotherapy for epilepsy and to identify patient and clinical characteristics predictive of optimally effective stabilized monotherapy doses. Of 406 randomized patients, 244 comprised the evaluable-for-efficacy population (12 weeks of treatment and stabilized topiramate dose during final 28 days); 213 were on topiramate monotherapy at the end of the trial. The mean stabilized daily dose of topiramate over the last 28 days of treatment (primary endpoint) was significantly lower for patients reporting one to three seizures (low seizure frequency, n=147) than for those reporting more than three seizures (high seizure frequency, n=66) during a 3-month retrospective baseline period (191 mg vs 239 mg, P=0.003). Patients in the low-seizure-frequency group reached a stable topiramate dose after a median of 36 days, compared with 53 days for patients in the high-seizure-frequency group. Linear and stepwise regression analyses showed baseline seizure frequency and lifetime seizure count to be significant (P<0.05) predictors of the stabilized dosage. Most treatment-emergent adverse events (TEAEs) were mild to moderate; those occurring with cumulative incidence rates >10% in either seizure frequency group were paresthesia, fatigue, anorexia, dizziness, somnolence, headache, and hypoesthesia; 18.2% of patients discontinued topiramate because of a TEAE, 5.1% reported serious TEAEs, and no deaths were reported during the study.