Positron emission tomography has offered the possibility to investigate the pathophysiology of idiopathic generalized epilepsies. Absence epilepsies demonstrate normal cerebral glucose metabolism and benzodiazepine receptor density. Conversely, juvenile myoclonic epilepsies are associated with frontal hypometabolism, which aggravates during a working memory task. Typical 3 Hz spike and wave discharges lead to a diffuse hypermetabolism. The latter resembles that observed during GAERS rats absences, and clearly differs from the hypometabolism encountered in partial epilepsies associated with generalized spike and wave discharges. Overall, functional imaging data provide further evidence of syndromic specificities in idiopathic generalized epilepsies.