Positron emission tomography (PET) is currently used in the presurgical workup for drug-resistant partial epilepsies in addition to MRI. Interictal metabolism is studied in clinical practice using (18)fluoro-desoxy-glucose ((18)FDG). In medial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis, hypometabolism ipsilateral to the epileptogenic focus is found in 70-90% of cases. However, hypometabolism is larger than the structural lesion observed on MRI and includes the epileptogenic zone and ictal discharge spread areas. Hypometabolism is related to surgical outcome and cognitive disturbances in MTLE. Although the usefulness of PET appears less well-established in extratemporal lobe epilepsy and in children, its sensitivity may be improved by coregistration and superimposition of PET on MRI at any age. Focal hypometabolism can be easily detected by visual analysis, allowing detection of minor gyral abnormalities that may correspond to focal cortical dysplasias. Moreover, in cases of negative MRI, focal hypometabolism findings may help invasive monitoring planning and deep electrode placement for SEEG, and finally improve surgical outcome.