In the preoperative evaluation of refractory epilepsy, two aspects need to be performed, namely, to determine the site of epileptic origin and to identify the area responsible for brain function in order to achieve a cure of seizures and to protect brain function after surgical treatment. In a small number of patients, where these two goals cannot yet be effectively achieved with other noninvasive tests, intracranial placement of electrodes for examination is required. Intracranial electrodes are at the forefront of technology in the field of epilepsy treatment. We have recently performed intracranial EEG in selected patients. The analysis of intracranial EEG recordings and a series of related tests ultimately led to the optimal treatment of the patients in terms of treating seizures and not bringing about functional deficits.