To present updated aspects of the Infectious Mononucleosis caused by the Epstein-Barr Virus.Research of bibliographic references through the Medline and direct research of selected papers.A concise approach to some aspects related to the epidemiology of the virus, namely the two types that are presently known,EBVtypeAandEBVtype B, and some differences that they present. It was possible to establish a relationship between what one sees in the clinical picture and the immunological changes that occur at the same time. The author also describes the physiopathology, clinical features, complications and other syndromes associated to the EBV. As far as the laboratory workup is concerned, it is important to have a complete blood count as the first step, followed by the quantitative exam of the heterophile antibodies and antibodies antiEBV analysis.The pathologies related to the EBV are important, and certainly fascinating from the immunological point of view. Among these, the Infectious Mononucleosis caused by the EBV has shown some interesting clinical and laboratorial aspects.