The research in this thesis was conducted with the fundamental goal of determining the basic implications of demographic aging on the sustainability of the existing pension system. Croatia's demographic picture is marked by three trends that are becoming stronger every year, which include natural depopulation, negative migration balance, and an aging population. These trends have a strong impact on all dimensions of social security, and they are particularly pronounced in their impact on the pension system. Namely, the decreasing number of live births also means that in the next generations there will be a significant decline in the influx of young people into the labor force, and on the other hand, from Croatia every year an increasing number of young people emigrate in search of work and better living conditions. Consequently, there is an increasing decrease in the share of persons aged between 15 and 64 (working age) in the total population. At the same time, under the influence of increasing life expectancy, the Croatian population is getting older, and the length of use of the right to a pension is constantly growing, which puts an increasing burden on the pension system. Croatia has undergone several pension reforms so far, and a new one is being prepared, because of the current situation in which as much as 42% of pension payments are settled from the state budget, and 1.25 insured persons work for the pension of one pensioner, is unsustainable in the long run. The aging population and the prolongation of people's life expectancy is further exacerbated by increasing pressure on the pension system as the period of exercising the right to a pension increases from year to year. Another problem in Croatia is the fact that a large percentage of workers use the right to early retirement, and the possibility of remaining in the labor market even after acquiring the right to retire benefits from a very low share of the Croatian population up to 69 years of age. In contrast, European practice has shown that developed countries are increasingly encouraging the elderly to stay in the labor market and this option is emerging as one of the most prominent options that could be used more and more in the future.