Six epileptic women, showing a clear increase in seizure frequency in the perimenstrual period, were studied during three consecutive menstrual cycles. At each control seizure occurrence, EEG recordings, endocrine profile and antiepileptic drug plasma levels were evaluated. The only pathological finding was the progesterone deficiency with a relative hyperestrogenism during the late luteal phase. Our data agree with other reports suggesting that catamenial epilepsy may result from a sex hormone disregulation.