In this thesis the impact of population aging on the sustainabilty of the healthcare system in the Republic of Croatia is presented. The demographic aging process has affected the entire population of the Republic of Croatia. Such negative trends create great pressure on the country's healthcare system and represent a major challenge when it comes to its long-term sustainability. The thesis explains the structure of the health care system, the method of financing it, as well as the cause of the emergence of current problems. Furthermore, demographic trends are analyzed and the projection of the analysis of demographic aging on the sustainability of the health care system is presented. What policy measures are needed to make the current system sustainable and is it achievable? The analyzes carried out in this thesis led to the conclusion that the financing of the healthcare system of the Republic of Croatia is absolutely unsustainable and that the implementation of a new reform that will be determined by law is necessary. However, all reforms may slow down costs in the short term, but in the long term, health spending will continue to grow. Due to the accelerated aging of the population, health financing will become more and more a problem of economic policy over the years, and the expectations of the population about the scope of health care will become less and less achievable.