We measured local cerebral metabolic rate for glucose (ICMRGIc) using positron emission tomography (PET) in six children with Sturge-Weber syndrome (SWS) and in six neurologically asymptomatic children with facial capillary hemangioma suggestive of SWS. Children with advanced SWS showed markedly depressed ICMRGIc in the anatomically affected cerebral hemisphere in a distribution that extended beyond the abnormalities depicted on computed tomography scan. In two infants with SWS and recent seizure onset, interictal PET revealed a paradoxical pattern of increased ICMRGIc in the cerebral cortex of the anatomically affected hemisphere. In one of these infants, ICMRGIc was also increased in the contralateral cerebellum, suggesting activation of the cortico-ponto-cerebellar circuitry. Subsequent PET (28 months later) in this child revealed the typical ICMRGIc pattern seen in advanced SWS. Further study of this transient ICMRGIc increase may be important in disclosing the pathogenesis of unilateral cerebral degeneration in SWS. In neurologically asymptomatic children with the facial stigmata of SWS and in children with early SWS, PET provides a sensitive measure of the extent and degree of cerebral metabolic impairment. Serial PET studies in children with SWS can be used to assess disease progression and, together with computed tomography or magnetic resonance imaging, may be useful in the selection of suitable candidates for cerebral hemispherectomy or focal cortical resection.