Since the early 1970s, childhood vaccination has prevented millions of illnesses and tens of thousands of deaths. For these health benefits to continue, high levels of vaccination coverage must be attained for each new birth cohort and must be monitored to ensure protection from disease, to characterize undervaccinated populations, and to evaluate effortsto increase coverage. The National Immunization Survey (NIS) provides ongoing national estimates of vaccination coverage among preschool-aged children for the 50 states and 28 selected urban areas. For this report, NIS data collected during 2000 were compared with 1999 data; findings indicate that, during 2000, significant increases were reported on the national level of vaccination coverage with varicella and hepatitis B, and small but statistically significant decreases were reported in coverage with diphtheria, and tetanus toxoid, and pertussis vaccine. Coverage with poliovirus vaccine, Haemophilus influenzae type b vaccine, and measles-mumps-rubella vaccine were not significantly different from 1999. As in previous years, coverage varied among states. To maximize coverage among preschool-aged children, vaccination providers should continue to apply such strategies as reminders and recalls.