Medically intractable epilepsy, defined as the clinical attacks occurring at least once a month in spite of appropriate antiepileptic drug treatments, is one of the commonest disorders in the clinical neurology. Since surgical treatment of epilepsy is successful in selected patients, it is most important to delineate the epileptogenic focus and functions of adjacent cortical areas as precisely as possible. Recent advances in electrophysiology, magnetoencephalography, magnetic resonance imaging (MRI), functional imaging techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) have enabled us to elucidate the epileptogenic focus noninvasively without involving the conventional invasive EEG recording techniques. We evaluated 37 patients with intractable partial seizures by using prolonged video/EEG monitoring with sphenoidal or T1/T2 electrodes. MRI, ictal and interictal SPECT for blood flow measurement and interictal FDG-PET for glucose metabolism. Among 20 patients with intractable epilepsy who had a single ictal focus, PET, ictal SPECT and MRI findings were correlated with the ictal EEG finding with the concordance rate of 100, 86 and 75%, respectively. If all of those findings were convergent upon a single focus, then the surgical treatment with intraoperative corticography is most likely effective without employing any invasive recording. If those findings were divergent, then the invasive evaluation will be indicated.