The Epstein-Barr virus (EBV) is the best characterized human virus known to infect most people all over the world. In most cases, primary infection with EBV is asymptomatic and the virus persists life-long without causing any disease. The availability of sensitive detection methods, however has led to the identification of a wide array of EBV-associated disease entities. Although nearly 9000 publications have been written since the first description of this virus in 1964, many questions concerning its function and infection patterns remain unanswered. The direct involvement of EBV in the pathogenesis of a disease has only been established for infectious mononucleosis and lymphoproliferative disorders in the setting of congenital or acquired immunodeficiency. Extensive investigations on the role of EBV infection in the pathogenesis of all other EBV-associated lymphoid and epithelial proliferations have led to the conclusion that EBV is not the primary causative agent but it can promote tumour development. Since the early steps in neoplastic development are difficult to assess, further studies are required to clarify the precise role of EBV infection. Furthermore, the clinical significance of the presence of EBV in neoplasia is largely unknown.