Pčinja county is an administrative region bordering Bulgaria, Macedonia and Kosovo, and is featured by a number of demographic peculiarities and extremes. In Central Serbia, this county is certainly the region with the most heterogeneous ethnic distribution; this fact determines differences in fertility transition and the speed of demographic ageing. Almost 90% ethnic Albanians from Serbia inhabit the Pčinja county, and so do 40% of ethnic Bulgarians. In addition, this county is featured by strong intra- and inter-regional demographic differentiations, both spatial and structural. Reduction of polarization of demographic development in Serbia at macro and intermediate levels (excluding the Kosovo territory), as well as minor differences between urban and rural environments, have made the county rather specific. Thus this relatively small province includes the one with the highest fertility rate and with the youngest population in the entire Republic of Serbia, five levels of demographic age in only seven administrative entities, the municipalities with the highest and the lowest international migration, a concentration of municipalities with the highest masculinity, municipalities with extremely high illiteracy rates, municipalities without atheists, and so on. Common features of this demographically heterogeneous province are underdevelopment and poverty. They do not manifest in the same way all over the territory; they are rather modified by various cultural factors. .