Adult aged between 18 years and 74 years

Focal epileptic seizures with or without secondary generalization

Present treatment with one or two antiepileptic drugs (constant dosage during 8 weeks baseline phase prior to initiation of treatment with zonisamide). Stimulation of the vagus nerve is permitted and will not be counted as antiepileptic drug.

For women of childbearing potential (postmenopausal for more than 1 year): possible pregnancy during the study can be excluded (by hysterectomy, sterilization or simultaneous application of two recognized methods of contraception (no oral contraceptives only)

For male patients with partners of childbearing potential: a safe method of contraception is practiced during their study participation

Written consent to participate in the study

At least 6 focal or clonicotonic seizures documented completely in a seizure diary or the patient chart during the 8 prospective or retrospective weeks baseline phase.

Epileptic state during the past year

Non-epileptic fits

Generalized epilepsy

More than 4 weeks of seizure freedom during baseline phase

Concomitant progressive CNS disease including progressive myoclonus epilepsy

Concomitant treatment with vigabatrine and / or topiramate

Hepatic and/or renal insufficiency (creatine > 2mg% or GPT > 2 times ULN)

Body weight <= 40 kg

(History of) kidney stones; erythrocyturia, family history (in parents, children, brothers and sisters or grandparents) of kidney stones

(History of) drug and/or alcohol dependence

Active psychosis

Suicide attempt during the past 3 years

Pre-treatment with zonisamide

Known hypersensitivity to sulfonamides

Concomitant treatment with neuroleptic drugs

pregnant or breast feeding woman

participation in another therapy study within 3 months prior to or during this study

blood donation planned during or within 4 weeks after the participation in this study

elective surgery planned during the participation in this study

patient is not willing or not capable to meet the study demands

patient does not agree to the forwarding of his/her pseudonymous data

patient without legal competence

More than 4 consecutive weeks of freedom from seizure during baseline phase