Recent reports demonstrated that patients with medically intractable epilepsy were benefited with surgical treatments. Even in pediatric patients, early surgery is effective not only in seizure control but also in verbal, intelligent and social outcomes. In the present study, basic and clinical approaches in the treatment of intractable epilepsies were studied. In chronic cat model of intractable temporal lobe epilepsy induced by a microinjection of kainic acid, temporal cortical excision with amygdala focus resection or focus and hippocampal resections were examined by means of microsurgical technics. The cats with amygdala focus resection demonstrated spontaneous hippocampal seizures while cats with focus and hippocampal resection did not show seizures in the long time course after the surgery. In a cat model of cortical focal seizures, multiple subpial transection(MST) was examined. The cortical seizures, induced by a microinjection of kainic acid into unilateral sensori-motor cortex, were suppressed immediately after the MST. Postoperative course was uneventful and seizure was not recurred. However, pathological study demonstrated subpial scar formation at the site of MST in the sensori-motor cortex. In 38 patients with medically intractable epilepsies, surgical treatments were performed in the Department of Neurosurgery. Asahikawa Medical College. The site of the epileptogenic lesion was studied with Video-EEG longterm monitorings, Neuro-imagings with CT, MRI, interictal SPECT and/or ictal SPECT. At the surgery, intraoperative electrocorticograms(ECoGs) were monitored under light neuroleptanalgesia in order to localize epileptic focus. Seizure free rate with or without postoperative medication was 72%. Remarkable improvement was observed in 7 patients (18%), but, 4 patients (10%) did not show any improvement.