AIM:To characterise patients treated with zonisamide in everyday practice and describe the effectiveness and tolerability of treatment. METHODS:This was an observational, longitudinal, naturalistic study, conducted by neurologists in France. Patients who had started zonisamide treatment at least three months prior to inclusion were eligible. Data were collected at routine consultations at inclusion (Visit 1) and three to six months later (Visit 2). At Visit 1, investigators documented epilepsy-related variables based on patient records before initiation of zonisamide and at inclusion. At Visit 2, the investigators re-evaluated seizure activity and rated effectiveness. Adverse events were also documented. RESULTS:A total of 428 patients were included in the study based on evaluation by 132 neurologists. Zonisamide was initiated at a daily dose of 50 mg and 25 mg in 61% and 31.8% of patients, respectively. The median maintenance dose was 300 mg/day. Prior to initiation of zonisamide, the mean seizure frequency was 16.0 seizures/month. This was reduced to 8.7 seizures/month at Visit 1 and to 7.1 seizures/month at Visit 2. The response rate and proportion of seizure-free patients was 61.9 and 31.1% at Visit 1 and 65.9 and 25.6% at Visit 2, respectively. The frequency of seizures at Visit 2 decreased significantly (p<0.05) for all seizure type subgroups, except for simple partial seizures. Responder rates were >60% for all analysed subgroups. The proportion of seizure-free patients was significantly higher in patients receiving bitherapy, compared to the others (p=0.007). The most frequently reported adverse event was somnolence (5.1%); three serious adverse events were reported. CONCLUSION:In everyday practice, zonisamide is principally used in association with other antiepileptic drugs for the treatment of focal epilepsy in adults. It is effective in improving seizure control and quality of life, and is generally well-tolerated.