Vaccination is one of the most powerful means to save lives and to increase the level of health of mankind. However, the impact of immunization against the most threatening infectious agents on life expectancy has been the object of a still open debate. The main issues are: the relative influence of nutrition and infectious diseases on demographic patterns of populations; the possibility that lives saved thanks to vaccination are subsequently lost due to other competing causes of death; the positive indirect effect of immunization on other causes of death. With regard to past evidence, several data from the United Kingdom and Scandinavian countries show that the widespread use of smallpox vaccination starting at the beginning of the nineteenth century resulted in a marked and sustained decline not only of smallpox-related deaths, but also of the overall crude death rate, and contributed greatly to an unprecedented growth of European population. As to the present, it is estimated that 3 million children are saved annually by vaccination, but 2 million still die because they are not immunized. Tetanus, measles and pertussis are the main vaccine-preventable killers in the first years of life. Data from Bangladesh show that full implementation of EPI vaccines has the potential of reducing mortality by almost one half in children aged 1-4 years. Recent progress in the development of vaccines against agents responsible for much mortality in the developing countries make it possible to forecast a further substantial reduction of deaths for infectious diseases in the next century.