Catamenial seizures are defined as epileptic seizures occurring during distinct phases of the menstrual cycle (i.e., periovulatory, premenstrually and during menstruation). The cyclic changes of the gonadotropic hormones are thought to be the main cause of the seizures. This hypothesis is supported by results of animal experiments, which have shown oestrogens to increase neuronal excitability whereas progesterone lowered it. We investigated 21 women with epilepsy who reported a catamenial increase in seizure frequency. Only 24% of these women actually exhibited a catamenial manifestation in more than 75% of seizures. The incidence of catamenial seizures is reported in the literature to be between 10% and 72%. Catamenial seizures are treated with anticonvulsant drugs. However, when anticonvulsants have failed to suppress seizures, progesterone or progesterone-derivates have been administered with success. We treated 16 patients with a synthetic GnRH-analogue to suppress the hormonal release of gonadotropins. Four of the six patients with only catamenial seizure manifestations and no other seizures became seizure free. Ten patients had catamenial seizures as well as seizures not related to the menstrual cycle. A decrease in seizure frequency by more than 50% was achieved in 7 of these 10 patients.