A prospective cohort analysis of premenopausal women with focal epilepsy was conducted in order to determine whether polycystic ovary syndrome (PCOS) is a common finding in women treated with antiepileptic drugs (AED). This study was carried out in 93 of 150 women (aged between 20 and 53 years; mean, 34.3 years) with chronic focal epilepsy consecutively cared for at the Department of Epileptology, University of Bonn: 38 were receiving one AED (18 valproate, 20 carbamazepine), 36 more than one drug, and 19 were without medication. Patients were followed-up for 6 months. PCOS was defined as hyperandrogenism (testosterone concentration, > 0.7 ng/ml) combined with oligomenorrhoea (cycle length, > 35 days) or amenorrhoea. PCOS was identified in two out of 19 (10.5%) patients receiving no medication; in four of 38 (10.5%) of patients receiving monotherapy, and in none of the patients receiving more than one AED. The incidence of PCOS in patients treated with valproate monotherapy (11.1%) was similar to that in patients treated with carbamazepine (10%) and also to that in patients not treated with AEDs. The results of this study suggest that the manifestation of PCOS in women with focal epilepsy is not related to the administration of valproate or carbamazepine.