From the demographic point of view, the future of Serbia's population is relatively certain at least in the next three to four decades. However, the decreasing and ageing of the population are considered to be very certain processes in the much longer term. Although replacement fertility is an essential condition for long-term survival of any population, it is shown that only an immigration impulse could enable desired effects of the potential fertility recovery in Serbia in the longer perspective. Such a migration transition (from net emigration to net immigration) would inevitably lead to increased socio-cultural diversity and require the development of integration strategies. If successful, policies to stimulate an increase in net migration provide an almost instant result. Apart from old immigration countries from Western Europe, this was the case with new immigration destinations located in Mediteranean and Central Europe, including some former socialist countries. When evaluating the future trend of international migration balance of Serbia, the experiences of the latter countries is used. The population dynamics model created for the purpose of the paper is based upon the probabilistic concept of projecting vital components. The main conclusion is that there is no demographic alternative to the migration transition in Serbia when it comes to sustainability of the social security systems in the coming decades, but the realization of such a scenario is still not clear from today's perspective, given the existing limitations of the socio-economic nature.