Patients with focal epileptic seizures with or without generalization who are at present treated with one or two antiepileptic drugs are eligible for this study, provided that they fulfill all inclusion criteria and none of the exclusion criteria. Following a baseline phase of 8 weeks duration, the patients are randomised and they receive an initial daily dose of 50 mg zonisamide during the first week. The daily dose is then increased to 200 mg zonisamide in group A or 400 mg zonisamide in group B, respectively. After eight weeks of treatment, the daily dose in group A can be increased to 300 mg in case of insufficient efficacy. Control assessments are performed at the beginning of the study and at the end of the prospective baseline phase, if applicable and after 4, 8, 12, and 16 weeks. At the end of the first, second, and third treatment week, and at the end of week six, the patient is additionally contacted by telephone. Efficacy and safety parameters are assessed at baseline, during all control visits, and at the end of the study.