The purpose of this statement is to inform physicians of a modification in the recommendation of the appropriate age for routine administration of the second dose of measles-mumps-rubella (MMR) vaccine. The implementation of the two-dose measles vaccine schedule has improved the control of measles, but some outbreaks continue to occur in school children, although ≤95% of children in school have received one dose of vaccine. Because most measles vaccine failures are attributable to failure to respond to the first dose, that all children receive two doses of measles-containing vaccine is essential for the control of measles. Routine administration of the second dose of MMR vaccine at school entry (4 to 6 years of age) will help prevent school-based outbreaks. Physicians should continue to review the records of all children 11 to 12 years of age to be certain that they have received two doses of MMR vaccine after their first birthday. Documenting that all school children have received two doses of measles-containing vaccine by the year 2001 will help ensure the elimination of measles in the United States and contribute to the global effort to control and possibly eradicate measles.