On 16–17 March 2000, the National Immunization Program of the Centers for Disease Control and Prevention convened 12 consultants and 10 resource specialists to review the present status of measles in the United States and to provide individual opinions on 4 questions: Is measles currently endemic in the United States? If current information is not sufficient to make such a determination, what additional information is needed? Is it possible or desirable to establish a precise definition of "elimination"? What elements of the US immunization program should be modified or strengthened to achieve/maintain elimination?