Converging evidence suggests that partial epileptic seizures can cause a circumscribed increase of CBF. However, quantified studies of ictal perfusion changes verified by intracranial EEG are still needed to better evaluate the relationships between CBF changes and the underlying electrical activity. We studied, in 10 patients undergoing a SEEG for epilepsy surgery, the local perfusion changes measured by [15O]-H2O PET during focal epileptic discharges induced by intracerebral electrical stimulation. CBF measurements under SEEG control were performed at rest and during stimulations eliciting, or not, subclinical or mild symptomatic epileptic discharges. PET and magnetic resonance imaging slices parallel to the AC-PC plane were matched for anatomical identification of cortical regions. Individual normalized CBF difference images between rest and stimulation (with or without induced discharge) were analysed by a hierchical description and multiscale detection method. Only CBF changes at p < 0.01 were considered significant. No significant CBF change was observed on test-retest at rest or during ineffective stimulations. Among the 12 elicited discharges, of which 11 involved mainly the temporal lobe, 8 were associated with a focal CBF increase (16-55 p. 100), there was no CBF change in 3, and a significant CBF decrease was observed in 1 (64 p. 100). These latter 4 discharges were restricted to mesio-temporal lobe structures. PET data were analysed in the same 10 anatomical areas during each of the 12 discharges. In 70.5 p. 100 of the 61 regions explored by SEEG, PET and depth EEG findings were consistent, showing either a CBF change in a discharging area, or no CBF change in a region unaffected by the discharge. Areas of increased CBF indicated an underlying epileptic discharge in almost 100 p. 100 of the cases. Discrepancies between SEEG and PET concerned almost always discharging regions showing no ictal CBF changes. A focal CBF increase detected at the seizure onset is a reliable marker of an underlying epileptic discharge. However, the extent of the CBF changes can be more restricted than that of the electrical discharge, and ictal discharges restricted to the mesial temporal cortex can be overlooked by CBF studies.