Epstein-Barr virus (EBV) is a human viral pathogen of considerable importance. More than 95% of the human population world-wide becomes infected with the virus during childhood, although in the West infection may be delayed until adolescence. The infection only has an undesirable significant clinical outcome in a tiny minority of cases, but because the virus is so ubiquitous the minority is numerically very significant. The virus is associated with two important human cancers, endemic Burkitt's lymphoma (BL) and undifferentiated nasopharyngeal carcinoma (NPC). These diseases have a very clearly defined geographical distribution in the Third World indicating a strong co-factor dependence. In the West, Epstein-Barr virus infection, when delayed to adolescence, is associated with infectious mononucleosis. The virus is also associated in the West with tumours arising in individuals undergoing immunosuppressive treatment or who are immunosuppressed as a result of HIV infection. More recently evidence has been obtained of an association with Hodgkin's disease which is very common in the West. A number of vaccines have been developed based on the EBV envelope glycoprotein gp340. Vaccination of those populations at risk from developing NPC or BL should lead to a reduction or elimination of these diseases. A safe and effective vaccine may also have a role in the prevention of EBV-related diseases in the West. Recombinant vaccinia, varicella and adenovirus vaccine vectors expressing gp340 are being developed and a recombinant-derived subunit vaccine based on the gp340 molecule is shortly to enter phase I human trials.