Summary: To date, 1,809 individuals have been exposed to topiramate (TPM), primarily adults with partial-onset seizures. Of this total, 665 patients have been treated for more than 1 year, 177 for more than 3 years, and 67 for more than 5 years. The profile of treatment-emergent adverse reactions (TEAEs) observed with TPM at various dosages is based primarily on data from five double-blind, placebo-controlled trials in which 360 patients received TPM at target doses of 200–1,000 mg/day. Long-term safety is assessed on the basis of 1,001 patients treated with TPM in controlled and open trials for up to 5.3 years. Most of the commonly reported TEAEs were related to the central nervous system and were observed with greater frequency at dosages above the 200–600-mg/day range found to be optimal in dose ranging trials. Nephro-lithiasis not requiring surgery was seen in 1.5% of patients, and mild, dose-related weight loss was associated with TPM therapy. No clinically significant treatment-related abnormalities were observed in clinical laboratory parameters or in neurologic, electrocardiographic, oph-thalmologic, or audiologic tests.