Postictal psychosis is a rare complication of epileptic seizure characterized by reversible psychotic symptoms after flurries of seizure attack. It has been attributed to a phenomenon similar to Todd's paralysis without definitive proof. We studied regional cerebral blood flow (rCBF) of six patients with postictal psychosis by (99m)Tc-HMPAO SPECT scan. Baseline rCBF was compared with the rCBF during postictal psychosis. An asymmetry index (ASI) was calculated as 200 x [(ipsilateral ROI count density - contralateral ROI count density)/(ipsilateral ROI count density + contralateral ROI count density)] %. Significant differences could be found between ASIs during postictal psychosis and interictal state SPECT scan over the lateral temporal neocortex region (P = 0.017). Although hyperperfusion abnormality in SPECT can be found in Todd's paralysis, such findings are more commonly found in cerebral hyperactivity conditions. Taking into account the clinical characteristics of postictal psychosis, namely a preceding lucid interval and crescendo-decrescendo clinical course, these may be an alternative psychopathogenic mechanism for the development of postictal psychosis.