[en] Regional cerebellar blood flow was measured in a patient with left-sided ataxic hemiparesis, using single-photon emission computed tomography and N-isopropyl-p-[¹²³I]Iodoamphetamine. X-ray computed tomography revealed a small infarct in the paramedian portion of the right upper basis pontis. Blood flow was markedly reduced in the contralateral cerebellar hemisphere corresponding to the side of ataxia. The present study emphasizes the value of the three-dimensional functional imaging of the cerebellum to investigate the responsible lesion for ataxia and to study function of the cerebro-cerebellar circuits