Purpose: To investigate the various ictal perfusion patterns and find the relationships between clinical factors and different perfusion patterns. Materials and Methods: lnterictal and ictal SPECT and SPECT subtraction were performed in 61 patients with partial epilepsy. Bath positive images showing ictal hypoperfusion and negative images revealing ictal hypoperfusion were obtained by SPECT subtraction. The ictal perfusion patterns of subtracted SPECT were classified into focal hypoperfusion, hypoperfusion-plus, combined hypoperfusion-hypoperfusion, and focal hypoperfusion only. Results: The concordance rates with epileptic focus were 91.8% in combined analysis of ictal hypoperfusion and hypoperfusion images of subtracted SPECT, 85.2% in hypoperfusion images only of subtracted SPECT, and 68.9% in conventional ictal SPECT analysis. Ictal hypoperfusion occurred less frequently in temporal lobe epilepsy (TLE) than extratemporal lobe epilepsy. Mesial temporal hypoperfusion alone was seen only in mesial TLE while lateral temporal hypoperfusion alone was observed only in neocortical TLE. Hippocampal sclerosis had much lower incidence of ictal hypoperfusion than any other pathology. Some patients showed ictal hypoperfusion at epileptic focus with ictal hypoperfusion in the neighboring brain regions where ictal discharges propagated. Conclusion: Hypoperfusion as well as hypoperfusion in ictal SPECT should be considered for localizing epileptic focus. Although the mechanisrn of ictal hypopertusion could be an intra-ictal early exhaustion of seizure focus or a steal phenomenon by the propagation of ictal discharges to adjacent brain areas, further study is needed to elucidate it. (Korean J Nucl Med 2000;34:169-82)