Neurological manifestations of viral diseases are predominantly secondary to herpes viridae infections. Among them Epstein-Barr (EBV) infections are rare particularly in immunocompetent adults. A 52 year old right-handed woman was admitted for progressive walking difficulties. She presented a proximal limb weakness with proprioceptive ataxia and pain because of lumbosacral radiculopathy confirmed by electromyography. Drowsiness and mnesic troubles were explained by encephalitis on electroencephalography. Brain MRI showed an enhancement of the sub-arachnoïd spaces. The diagnosis of meningoencephaloradiculitis due to primary EBV infection was supported by a mononucleosis syndrome, an increased antibody level and positive EBV PCR in the CSF. Clinical features spontaneously improved without antiviral treatment. Primary EBV infections are rare in adults, as more than 95p.cent of them are positive for EBV serology after 20 years of age. EBV PCR is CSF in an important diagnostic tool allowing to stop antiviral therapies in these cases having a good prognosis.