The aim of a Stereo-EEG investigation is to verify and prove that the hypothesis, done on the basis of the preliminary investigations (clinical, EEG, neuroradiological), are correct. This task is particularly hard in frontal lobe epilepsies, because of anatomical and physiopathological reasons. Among 277 consecutive patients, 86 were explored for a probable frontal epilepsy. The stereotactically introduced electrodes. 1) simultaneously record the electrical activity on both, mesial and lateral cortical areas, and, 2) in 3/4 of cases also investigate extra-frontal, mainly temporal, areas. Two small, non-surgical haematomas were provoked in one patient. The spatial trajectory of the discharges, evaluated with this methodology, permits of limiting the surgical removal in many cases.