Acute cerebellitis occurrs in the absence of cerebral hemispheric involvement and is exceptionally rare. It is charac-terized by an acute onset of cerebellar dysfunction following a respiratory, gastrointesitnal infection or skin rash. However, almost all patients show good prognosis. We experienced two cases of acute cerebellitis in young adults. One patient was admitted due to gait ataxia and dysarthria. The immunological laboratory findings revealed an acute Ebstein Barr virus infection and an electronystagmogram showed a periodic alternating nystagmus. The other patient was admitted due to severe gait ataxia, with no identification of any organism. CSF examinations revealed elevated protein and brain magnetic resonance images showed cerebellar foliae enhancement bilaterally. Both patients recovered without any disabilities. J Kor Neurol Ass 17(3):403 ~ 406, 1999 Key Words : Cerebellitis, Epstein Barr virus, Periodic alternating nystagmus.