The first effective Haemophilus influenzae type b (Hib) conjugate vaccines were approved for use in children and infants between 1987 and 1990. In 1993, the federal government began the Childhood Immunization Initiative (CII), a program to improve the rate of vaccination of children nationwide. Subsequently, the proportion of 19 to 35-month-old children who received three or more doses of Hib vaccine rapidly increased from 28% in 1992 to 90% by 1995, with a concurrent dramatic decline in the incidence of H. influenzae meningitis. We reviewed cases of H. influenzae meningitis reported to the Wisconsin Division of Public Health from 1981 to 1997. The mean annual incidence of H. influenzae meningitis declined 96% from 2.4 cases per 100,000 persons in the pre-vaccination period (1981-1986) to less than 0.1 case per 100,000 persons after Wisconsin had achieved 90% Hib vaccination coverage (1994-1997). H. influenzae meningitis occurrence declined dramatically among all age groups, including 96% among children aged less than 1 year old, 99% among 1-4 and 5-9 year olds, and 46% among persons 10 or more years old. Consistent with national trends, the majority of H. influenzae meningitis cases reported in 1997 was caused by non-type b strains of H. influenzae.