New recommendations from the Immunization Practices Advisory Committee call for a second dose of measles vaccine for school age children. The purpose of this paper is to demonstrate the need for additional measures for the protection of preschool age children. A hospital-based measles outbreak of 25 cases in Kent County, MI, in 1990 provided an opportunity to study measles transmission to preschool age children. Twenty-two (88%) were people who had never received measles vaccine. Twelve of the cases were unvaccinated preschoolers, seven of whom were older than 15 months. Three nonvaccinated, but eligible people (one philosophic exemption and two vaccine-eligible preschoolers) were the source of most of the other cases. One school age unvaccinated child died of measles pneumonitis. A telephone survey indicated that improved public education regarding indications and contraindications to vaccination might encourage vaccination of children according to public health recommendations.