Epstein-Barr virus (EBV) is one of eight known human herpesviruses (HHVs). A primary EBV infection is generally subclinical in immunocompetent individuals, but often causes infectious mononucleosis (IM) in adolescents and adults, which is generally a benign and self-limiting disease. Therefore, in immunocompetent individuals only symptomatic treatment is recommended, although fatal or malignant diseases such as fatal IM, Burkitts lymphoma (BL) and nasopharyngeal carcinoma (NPC) may develop without obvious preceding immunodeficiency. However, in certain circum stances such as in patients with hereditary immunodeficiencies, in recipients receiving a potent immunosuppressant or in patients with acquired immunodeficiency syndrome (AIDS), this virus strongly links to the development of lethal lymphoproliferative diseases (LPD). These LPD range from IM-like illness associated with polyclonal proliferation to malignant lymphoma in monoclonal fashion. To date, no specific therapy has been available for latent EBV infection itself, but understanding the underlying pathogenetic mechanisms in each condition provides the possible treatment including anti-viral agents, immune modulators and chemotherapeutic drugs. Furthermore, severe combined immunodeficiency (SCID) mouse engrafted with human peripheral blood mononuclear cells is a suitable model for EBV-associated LPD which occur in human beings. Using this, several therapeutic trials have been investigated, and some are possibly beneficial. This concise review focuses on recent understanding of the pathogenetic mechanisms in various EBVassociated diseases in immunocompetent and immunocompromised individuals, and discusses potent therapeutic approaches in each condition.