Over the past three decades we have witnessed an evolution of the concept of security in general and of demographic security as a specific field of security studies. The approach to security has been changing both in regards to a widening of subjects and referent objects of security, and a widening of the security domain. Consideration of the demographic component in the security sphere has evolved in accordance with this development; the scope of perspectives through which demographic security is viewed and defined has expanded – the population composition, population dynamics and human capital paradigm. Aspects of demographics and security are in continuous interaction and interdependence which significantly determines demographic security and national security.The aim of this paper is to establish a specific link between demographic security and security in ten post-socialist countries of South Eastern Europe (SEE). In accordance with this aim, an analysis has been made of the compositional elements and population dynamics in order to determine demographic security of the observed states. The analysis indicates unfavourable demographic security, and negative demographic composition and dynamics in most of observed states, which suggests that demographic security will have a continuing negative impact on the security of the countries analysed and the region as a whole.