The National Immunization Survey is conducted by the National Center for Immunizations and Respiratory Diseases and the National Center for Health Statistics at the Centers for Disease Control and Prevention. It began in April 1994 in order to collect data on childhood immunization coverage. It uses a list-assisted random-digit-dialing telephone survey methodology of household respondents, and a mailed survey to children’s health care providers. The target population for the survey is children aged 19-35 months at the time of the interview, and the mail-in portion of the survey collects data on all current recommended vaccines and doses. Major changes to the 2002 survey included a revision to the random-digit-dialing sampling weights, and to the definition of children with adequate provider data, including in it those who are unvaccinated. In total, the survey produced complete interviews for 31,693 children, and adequate provider data for 21,410 of those children.