Systematic mandatory immunization of children against tetanus begun in Italy in 1968. Preceding birth cohorts, accounting for almost 80% of present Italian population, were poorly immune or totally non-immune; around 90% of cases of tetanus occurring in Italy in recent years are observed among them. In a national sample of 4770 young males born between 1956 and 1963, about one third was not protected. Prevalence of non-immune subjects was greater in the Southern Regions and the Islands, in rural areas, among the unemployed, among the older birth cohorts.