The paper analyses the phenomenon of extramarital births in Serbia in the period of 1950-2008. Great changes that European countries have been undergoing in the last half-century related to fertility and family forms were also followed by an intense increase in the share of extramarital births. This is also true for Serbia (excluding Kosovo), where the share of extramarital births in total live births for the period of 1950-2008 increased almost 3 times (from 8.0% to 22.8%), and their number increased by a fifth (from 13,1 to 15,7 thousand). At the beginning of the observed period, significant differences existed in the percentage shares of extramarital births in the main regions, with the share in Vojvodina several times that of Central Serbia. Subsequent divergent dynamics led to the disappearance of regional differences and, after 1970, the level of extramarital fertility was mostly balanced. From a European aspect, the increase in the share of extramarital births in Serbia was moderate, with Serbia being one of the few countries that also recorded a decrease in the share of extramarital births in the last four decades (between 1970 and 1980). In comparison with other European countries, position of Serbia changed during the observed period from the top towards the bottom of the list, so that it was in its lower half in 2008. During the 1990s, as well as at the beginning of the 2000s, the greatest increase in the share of extramarital births in Europe was recorded in countries in transition. In the paper, the changes in the marital status of the population were treated as one of the determinants of the increase of extramarital births in Serbia. The paper also points out the similarities and differences between births in cohabitation and marriage, and legal aspects related to extramarital unions and extramarital births were also analyzed. The conclusions about the degree of presence of births in stable partner unions were made indirectly, based on the results of survey research and the latest available data on recognition children by their fathers. Since approximately three fifths of extramarital children at the beginning of the 2000s were not recognized, it was assumed that they were born in unstable unions and that they were brought up by their mothers alone. At the same time, the small level of cohabitations, discovered through survey research on the representative sample, shows that the increase in extramarital births was not proportionally followed by an increase in cohabitation. Therefore, based on indirect indicators, the authors conclude that the phenomenon of extramarital birth in Serbia was not the result of an advanced transition in partner relationships and abandoning of marriage as the partner union in which children are born. At the same time, the importance of understanding the social context of births was pointed out on the example of the Czech Republic, as a country in transition.