Between 1984 and 1987 reported pertussis cases in North Carolina increased threefold. Pertussis immunization rates were examined for those years in three one-year cohorts drawn from a random selection of North Carolina birth records. The percentage of children immunized with three DTPs at eight months of age was 58.1, 58.6, and 56.7 for the three cohorts. Only 20.5 percent of 117 reported pertussis cases in children 9-36 months of age during the last 10 years were adequately immunized. The low pertussis immunization rate may have contributed to the recent increase in pertussis cases in North Carolina.