Measles in the United States has declined dramatically since the introduction of measles vaccine in 1963, but still remains an important pediatric problem. When given at age 15 months or later, the live, further attenuated virus vaccine provides durable immunity in over 90 per cent of vaccinees. Measles vaccine failure has been associated with the use of inactivated measles vaccine, vaccination before 1 year of age, and errors in vaccine handling. To minimize measles vaccine failure, health professionals should re-vaccinate children whose initial vaccination is likely to have been ineffective, and pay meticulous attention to vaccine handling.