Summary Two patients, 19 and 16 years old, were hospitalized with meningoencephalitis symptoms, initiated by a generalised epileptic crisis in one case and by a coma in the other case. None of the patients showed typical signs of infectious mononucleosis. In both cases clinical improvement spontaneously occured within few days. These meningoencephalitis were relied to an Epstein-Barr primary infection by a systematic Epstein-Barr virus (EBV) serology and, in one case, by the detection of EBV genome in the CSF. The value of viral genome presence in the CSF need to be discussed.