The initial goal of the national vaccine stockpile program was to establish a 6-month supply of all recommended childhood vaccines, to meet national demands if a manufacturing process was interrupted. When the first vaccine stockpiles were created in 1983, the childhood immunization schedule was much less complicated than it is today, and the first stockpiles included only measles-mumps-rubella, poliovirus, and pertussis vaccines, as well as diphtheria and tetanus toxoids. However, today's vaccine needs are much greater, and current stockpiles do not include all recommended childhood vaccines, partially because inclusion of vaccines that are universally recommended, fully implemented, and produced by a single manufacturer has been made a priority. Future planning must also consider substantially higher vaccine costs, the development of new combination vaccines, a wide range of production times, and changes in immunization recommendations. Expansion and strengthening of the national vaccine stockpile program are critical to protect against future disruptions in vaccine supply.