Multiple sclerosis (MS) is the most common inflammatory demyelinating and degenerative disease of the CNS. The cause of MS is unknown but environmental risk factors are implicated in MS. Several viruses have been proposed as a trigger for MS, and lately Epstein-Barr virus (EBV) has become the leading candidate. An infectious aetiology fits with a number of epidemiological observations in addition to the immunopathological features of the disease. In this review we will summarize the emerging evidence, which demonstrates a strong association between EBV infection and MS. The conundrum remains as to whether EBV is directly involved in the pathophysiology of MS, or alternatively if the immunopathology of MS somehow affects the regulation of EBV infection.