Haemophilus influenzae (Hi) causes a variety of severe clinical illnesses including meningitis, pneumonia, epiglottitis, and septic arthritis. In the prevaccine era (i.e., before 1988), Haemophilus influenzae type b (Hib) caused approximately 95% of the Hi invasive disease among children aged <5 years. In 1988, Hib conjugate vaccines were introduced for use among children aged 18 months-5 years; they were subsequently recommended for routine use in infants by the Advisory Committee on Immunization Practices (ACIP) in 1990. During 1989-1995, Hib invasive disease among children aged <5 years declined 95% nationally. To document the decline of Hib invasive disease and to examine the epidemiology of reported nontype b Hi invasive disease among children aged <5 years, CDC, in collaboration with the California Department of Health Services, analyzed reported cases in California from 1990 to 1996. This report summarizes the results of the analysis and documents the decline of Hib without an increase of nontype b Hi invasive disease among children aged <5 years.