Problem: Menstrual disorders, reduced fertility and sexual problems seem to be more frequent in women with epilepsy than in the general population. Most investigations concerning menstrual disturbances in epilepsy patients, however, are small and based on selected materials. We therefore wanted to investigate the frequency of menstrual disturbances in a large, unselected population of epilepsy patients. Methods: A retrospective, questionnaire study of a cohort of female outpatients, aged 18–45 was conducted. Each patient chose a close female friend who served as control, to optimise matching regarding age and lifestyle. Results: Answers were received from 265 patients and 142 controls. Menstrual disturbances were more frequent in patients with epilepsy (48.0%) than in controls (30.7%) ( P=0.004). Menstrual disturbances were more frequent in patients on polytherapy versus monotherapy ( P=0.049) and more frequent in patients with high seizure frequency (>5 seizures/year) compared to patients with a lower seizure frequency or those seizure free ( P=0.006). The frequency of menstrual disturbances was higher in patients on valproate compared to carbamazepine monotherapy ( P=0.045). Conclusion: This investigation confirms that women with epilepsy have an increased frequency of menstrual disturbances compared to women without epilepsy. In women with high seizure frequency and in those on polytherapy, the frequency of menstrual disturbances are further increased. The highest frequency of menstrual disturbances occurred in women using valproate.