Introduction: H. influenzae type b, S. pneumoniae and N. meningitidis were the leading causative agents of invasive bacterial diseases (IBD) among children of less than 5 years of age prior to the introduction of the H. influenzae type b (Hib) conjugate vaccine. A significant decrease of invasive H. influenzae diseases (IHD) occured in nations that implemented routine Hib vaccination in their national immunization program (NIP). Aim: The goal of this study was to describe the frequency and characteristics of pediatric patients with IBD before and after routine Hib vaccination was implemented into the Croatian NIP. Subjects and methods: A retrospective analysis of patient records from administrative databases for patients aged 0 to 18 with etiologically proven IBD at University Hospital for Infectious Diseases “Dr. Fran Mihaljević”. Results: A total of 1112 pediatric patients were analyzed. The patients were divided into three periods: first, prevaccinal (reference) and two postvaccinal periods. During the second period, a statistically significant change in proportion occured for N. meningitidis (p<0,05), S. agalactiae (p<0,05) and H. influenzae (p<0,0001). H. influenzae (p<0,0001) maintained this trend during the third period as well. Additionally, a decrease in Hib meningitis cases was noted (p<0,0001). Conclusion: The implementation of Hib vaccine in the Croatian NIP led to a significant decrease of IHD. S. pneumoniae and N. meningitidis are still the leading causative agents of IBD and thus the introduction of adequate pneumococcal and meningococal vaccine in Croatian NIP should be considered.