Most global estimates indicate that more than 1 million children a year die from acute measles. The actual number of deaths may, however, be considerably higher than this. In addition, the impact of delayed mortality as a result of measles infection is only now being realized. Many months after they contract measles, children continue to experience higher levels of mortality and morbidity than those who do not. Immunization of children against measles therefore prevents mortality and morbidity not only during the acute phase but also during subsequent months. The impact of measles immunization programmes may therefore have generally been underestimated. The effects of measles infection on children during the early months of life are more damaging than those experienced by older children. Children should therefore be immunized against measles as early in life as possible, given the limitations of existing vaccines.