|Immunization coverage is a key measure of immunization system performance. As stated by the World Health Organization, information on immunization coverage is used for a variety of purposes: to monitor the performance of immunization services at local, national and international levels; to guide polio eradication, measles control, and neonatal tetanus elimination; to identify areas of weak system performance that may require extra resources and focused attention; and as oneâs consideration when deciding whether to introduce a new vaccine. In order to obtain complete data on immunization system performance in USA, immunization coverage is measured by Nationalm Immunization Survey (NIS) conducted by the Centers for Disease Control and Prevention (CDC) since 1994. Two most commonly used immunization status measures in USA are âage-appropriateâ andâup-to-dateâ (UTD). Age-appropriate are applied to a population or cohort of children that varies in age, and the measure indicates the proportion of children who received adequate number of vaccines for their actual age. UTD immunization coverage generally indicates the proportion of children in a population with adequate immunization status at a certain age threshold or age range. Age appropriate and UTD immunization coverage using combination series at any age in South BaÄka County were never measured. We expected that the UTD immunization coverage at 6 months of age would be much lower than 95% and that at 12 and 24 months of age there would be high and satisfactory UTD coverage.