Zonisamide (Zonegran), a novel antiepileptic drug (AED) approved recently in Europe as adjunctive therapy for refractory partial seizures in adults, has been used extensively in Japan and the United States. A substantial body of clinical experience has accumulated over a 14-year period, allowing the properties and pharmacologic/clinical profiles of zonisamide to be clearly defined. Zonisamide is structurally distinct from other AEDs and has multiple and complementary mechanisms of action, which likely contribute to its efficacy across a broad range of epilepsy types. Zonisamide has a long T1/2 enabling once-daily dosing, linear pharmacokinetics and minimal interaction with other drugs; plasma levels of commonly administered AEDs and oral contraceptives are unaffected by concomitant zonisamide. Effective control of partial seizures (up to 51% decrease in seizure frequency) is attained at doses of >or=300 mg/day, and optimal titration and maintenance dosing schedules have been established. The adverse event profile is well defined; in common with most AEDs, most adverse events are central nervous system-related (e.g. somnolence, dizziness, tiredness). Adverse events may be minimised with appropriate patient management. Zonisamide therefore has many characteristics considered desirable in an AED and represents a valuable addition to the therapeutic options for treating epilepsy in Europe.