This study describes the epidemiological characteristics of infections caused by Haemophilus influenzae type b, according to available data obtained from the Epidemiological Service of the Croatian Institute for Public Health. The archives of the Clinic for Infectious Diseases Hospital Split was searched in order to obtain data on treated patients of this disease in the 1997th - 2013th year. Until the introduction of vaccination against Haemophilus influenzae type b in Croatia and other countries, H. influenzae was the leading cause of purulent meningitis, severe acute inflammation of the soft membranes of the brain and spinal cord in children from 3 months to 3 years old and a huge public health problem. The introduction of immunization has led to significant changes in public health and epidemiology of the disease. For obvious decrease morbidity in Croatia was needed two years since the introduction of vaccination, and the last five years, the reduction of incidence of invasive H. influenzae disease in children under five years of age is 100% - meaning that they are virtually eliminated. However, will it remain such a situation depends on the scope of compulsory immunization against Hib, which, according to the regulations must be above 95%. In adults, in clinical practice, and further, after the introduction of compulsory vaccination record suffering from invasive disease caused by H. influenzae, but in which also decreased morbidity. Achieving immunity by vaccination has led to some "progress" in microbiological picture. Thus, the increased resistance of H. influenzae to ampicillin (which is not caused solely by vaccination) and the occurrence of other types of diseases caused by H. influenzae (f). This work has demonstrated already a known fact that the most effective preventive measure vaccination and that, in diseases that are a public health problem for which there is no effective vaccine, the most profitable (from any point of view) to introduce vaccination.