Rasmussen's syndrome is a progressive childhood disease of unknown cause characterized by severe epilepsy, hemiparesis, mental deterioration, inflammation of one cerebral hemisphere, and brain atrophy. Computed tomography, single-photon emission computed tomography (SPECT), and magnetic resonance (MR) neuroimaging findings of 8 patients with pathologically confirmed Rasmussen's syndrome were evaluated retrospectively. All patients showed a predominance of the atrophy in the temporoinsular region and cerebral hemispheric alterations on MR images in a similar extension as seen on SPECT studies. Focal increase in regional cerebral blood flow was observed in the 4 patients presenting with epilepsia partialis continua at the time of hexamethylpropyleneamineoxime injection. Extensive cortical hypoperfusion was noted in the other 4 patients who received the injection during the interictal state. Cerebellar functional abnormalities were present in 6 patients, 2 of them with structural damage.