The aetiopathogenesis of multiple sclerosis (sclerosis multiplex – SM) is not yet fully understood. All we know is the this is a polyaethiological disease in which viral and bacterial injection plays a significant role. This article presents a critical review of the findings indicating the contribution of viral injections to the development of SM. Particular attention is paid to Epstein-Barr virus, JC virus, human herpes-6 virus, human type 1 T-cell leukemia, the SM-related retrovirus and the measles virus. The recently suggested link between SM and the MSRV, SM-related, retrovirus has been strongly emphasized by its discoverers but we have not managed to confirm it in our own studies where the MSRV was found to be present in healthy subjects as well. The hypothetical relationship between viral infection and SM pathogeneses has gained much support, however and further advancements in understanding the contribution of viral injections to the development of SM would surely help us to develop new methods of treating SM patients.