One or more interictal positron computed tomograms of 18F-fluorodeoxyglucose were obtained on 50 patients with partial seizure disorders. Ictal as well as interictal electroencephalographic (EEG) data were available for all 50 patients, with scalp, sphenoidal, and depth electrode recordings done on 27 and scalp and sphenoidal recordings alone on 23. Thirty-five patients demonstrated one or more abnormal interictal zones of hypometabolism, while combined EEG studies were localizing for 36. There were considerable disagreements between the location of metabolic deficits and the epileptic focus revealed by individual scalp and depth EEG recorded ictal and interictal epileptiform activity; however, there was good correlation between the site of focal hypometabolism and the epileptic focus determined by the combined results of all electrophysiological studies. When focal hypometabolism and focal nonepileptiform EEG abnormalities (i.e., slow waves and attenuation of fast rhythms) were both present in the same patient, their localization agreed completely. Metabolic and combined electrophysiological techniques both occasionally produced false positive as well as false negative results. When used together, the EEG can confirm that a hypometabolic zone is epileptogenic, while FDG scans may indicate whether an epileptic EEG focus represents a lesion or propagation from a distant site.