A 17-year-old male was admitted to our hospital complaining of fever, headache and nausea. On physical examinations cervical and inguinal lymphadenopathy and hepatosplenomegaly were noted. Neurological examination revealed meningeal signs. Blood examination showed slightly increased lymphocytes and atypical lymphocytes (1-4%), increased ESR, CRP (2+), slightly elevated EBV VCA IgG (X20), and normal EBV VCA IgM (less than X 10). Initial pressure of CSF was 195mmH2O, cells 46/3mm3, protein 50mg/dl. Slowing of back ground activity of EEG such as theta and delta wave was noted. CT scan revealed normal. During the course EBV VCA IgG elevated to X160, EBV VCA IgM elevated to X20. Slight respiratory disturbance, photophobia, and dysosmia were noted. One month later, clinical symptoms and laboratory data improved, the patient was discharged. Forty days after the discharge, headache was excerbated and increased CSF protein (100mg/dl) and pleocytosis (33/3mm3) were noted. The patient was readmitted to the hospital. After 2 weeks in the hospital, symptoms were diminished and laboratory findings revealed normal. During 2 years before the third admission he was asymptomatic and could enjoy the college life. At age 19, he was admitted to our hospital complaining of fever, headache and nausea. Neurologically slight meningeal irritation was noted. Blood examination revealed 1% atypical lymphocytes. EBV VCA IgG was elevated (X320) and EBNA was X80. CSF protein was slightly increased (52mg/dl). During the clinical course CSF protein was elevated to 105mg/dl and cell count to 502/3mm3 (N: L = 27: 409, with 66 atypical lymphocytes). Persistent hiccup was noted. After 50 days CSF findings were improved and he was discharged.(ABSTRACT TRUNCATED AT 250 WORDS)