The juvenile neuronal ceroid-lipofuscinosis (JNCL) is a recessively inherited progressive encephalopathy. We studied 21 JNCL patients with a duration of illness of 1 to 17 years by 99mTc-HM-PAO single photon emission computed tomography (SPECT) and correlated the findings with clinical parameters. All patients had at least one hypoperfused brain area, the median number of such areas was 5 per patient. Parietally, occipitally, and in the cerebellar lobes hypoperfusion was usually mild whereas it was temporally more severe. Right parietal hypoperfusion correlated to neurological dysfunction.