Positron emission tomography (PET) using 18F-labeled 2-deoxy- d-glucose was performed serially in 5 infants with idiopathic West syndrome. While tonic spasms persisted, 2 infants had hypometabolism in the bilateral temporo-parieto-occipital regions, which disappeared after cessation of spasms. In 2 other infants, PET revealed focal hypometabolism in the temporal region a few months after the disappearance of tonic spasms, but subsequent PET studies were normal. PET can detect transient metabolic abnormalities of the cerebral cortex which may be associated with the pathophysiology of West syndrome.