A 19 year-old man presented with pharyngitis and cervical lymphadenopathy, followed by vomiting and acute cerebellar ataxia. Serologic studies were consistent with a recent Epstein-Barr virus infection. Although contrast-enhanced brain computed tomography and MRI scans were normal, brain perfusion single photon emission tomography (SPECT) examination using 99mTc-HMPAO, performed on the 15th day of illness, showed marked cerebellar hyperperfusion, suggesting a diagnosis of acute post-infectious cerebellitis. After treatment with intravenous human immunoglobulin (IVIg, 2 g kg-1 over three days), progressive neurologic improvement occurred over two weeks. A brain SPECT study repeated after two additional weeks demonstrated a normal perfusion pattern. We conclude that brain perfusion SPECT examination is useful in identifying post-infectious cerebellitis and in monitoring its clinical course. In addition, IVIg may be helpful in treating this condition.