The concordance between the epileptogenic area as determined by intracranially recorded spontaneous seizure onset and that determined by electrically induced auras or seizures in 126 patients with medically intractable epilepsy was studied. Four to 11 multicontact depth electrodes were chronically implanted in patients as part of a preoperative investigation procedure. Localization of the epileptic area was obtained from the recording of three spontaneous seizures and from stimulation data including self-reported auras, seizures, and intracranial EEG afterdischarges recorded during an incremental stimulation sequence at all cortical pairs of contacts. Positive responses to stimulation were obtained in 63% of patients. Concordance between spontaneous and induced auras or seizures was greater than 90% with single unilateral foci and less with multiple foci. Stimulation data reliably predicted the resection area in unilateral and bilateral temporal foci but not in other locations. Afterdischarge thresholds were not reliable predictors of the spontaneous seizure focus. The intracranial stimulation procedure used appears to provide useful confirmatory and complementary localizing information in relation to that obtained from spontaneous seizures.