During 1989 and 1990 measles incidence increased sharply in the United States. We compared cases reported during these years with those reported between 1981 and 1988. Incidence increased 462% in 1989, and incidence in 1990 (11.2/100 000) was the highest in more than a decade. Although all ages were affected the greatest increases were in children <5 years and in adults. Incidence was 7- to 10-fold higher among racial/ethnic minority preschoolers than whites, and 80% of vaccine-eligible preschool age cases were unvaccinated. Complications occurred in 9418 (20.5%) cases, most frequently in young children and adults. Large urban outbreaks affecting predominantly unvaccinated preschoolers were common; 47% of all cases reported in 1990 were associated with 5 outbreaks. Reasons for the increased incidence are not clear. Current information suggests no change in vaccination coverage among pre-school age children or in vaccine efficacy. Continued surveillance and evaluation of epidemiologic and laboratory data are necessary. The most pressing need is to improve age-appropriate vaccination among preschool age children.
