Poliomyelitis, an infectious disease with acute and persistent flaccid paralysis is caused by poliovirus (types 1, 2 or 3), an enterovirus. The infection is asymptomatic in 95% of infected subjects. Most of the paralytic cases occur in adolescents or adults in the course of polio type 1 infection. In the prevaccination era, in countries with poor hygienic conditions, infection in early childhood was common, mostly asymptomatic, and immunity in the population prevailed. In developed countries polio often struck adolescents and adults taking its toll in paralytic disease. The introduction of vaccination with the Salk vaccine (IPV Inactivated Polio Vaccine) in the USA and in Europe in 1956 and with the Oral Polio Vaccine (OPV) developed by Sabin worldwide in the early sixties made it possible to control the epidemic in large geographic areas, but it could not eliminate the disease worldwide. Poliomyelitis is still endemic in Central Africa and in the Indian sub-continent. Acts of war led to the reduction in the vaccination rate in different geographic areas, and smaller epidemics with wild virus but also with reverted vaccine strains occurred. In some parts of the world the rate of vaccination also declined due to elimination of poliomyelitis, and it came to small epidemics of paralytic polio mainly caused by reverted vaccine strains circulating in the population. Reverted vaccine strains also remain a central problem in the eradication of poliomyelitis projected for 2005 by the World Health Organisation. A high vaccination rate, preferably with 3 doses of OPV in infancy or early childhood, and exact worldwide monitoring of cases is indispensable for the eradication. For the complete eradication of poliovirus the live vaccine OPV would have to be changed to an inactivated vaccine IPV worldwide. However, this is presently unachieveable, because of logistic problems and high costs.