Infectious mononucleosis is a clinical syndrome that is most commonly associated with primary Epstein-Barr virus (EBV) infection. The disease is characterized by fever, pharyngotonsillitis and cervical lymph node enlargement. EBV transmissioon occurs through exposure to infected saliva, often as a result of kissing. During the incubation period virus replication first occurs in the oropharynx followed by viremia. The acute illness is characterized by high viral loads in the oral cavity and blood accompanied by the production of immunoglobulin M antibodies against the EBV viral capsid antigen and extraordinary expansion of CD8+ lymphocytes directed against EBV-infected B-cells. Besides causing acute illness, EBV is associated especially with Hodgin lymphoma, various cancers and multiple sclerosis. There is no licensed vaccine for prevention and no specific antiviral treatment.