ENIn the Polish-Lithuanian Commonwealth, that is in the Grand Duchy of Lithuania as well, during the Early Modern Period magnates played a leading role in the State both politically and culturally or economically. Due to this fact and considerable archives as well, this social class has always been and still is an object of scholarly interest. It is particularly apparent within the scope of their activity in the above mentioned areas as well as with regard to such phenom- ena as a patron-client relationship, processes connected with denominational transformations, military activity, etc. On the other hand, the issue related to the functionality and composition of a magnate family, its duration and pro- creation possibilities, etc., has not been studied for a long time. Although some demographic data appeared in certain publications, they were not a result of systematic research. They were presented incidentally, on the margin of discussing other leading topics. Furthermore, earlier estimates of some demographic parameters performed during the Interwar Period embraced a widely understood nobility, i.e. magnates were included therein together with the nobles. What is more, the calculations were based on a small number of data derived mostly from genealogical narrative sources.So far, Polish systematic and advanced demographic research on the Old Polish family have been focused on lower classes for which statistical sources are available (mainly church certificates (metrics) and general censuses, and for the pre-certificate period - court municipal and land records). In West Eu- ropean research, however, where historical demography is a priority, all social classes have already been embraced by demographic analyses, including those that can be depicted as elites. Therefore, the presented work aims to complete a significant research gap in the Polish historiography, i.e. present the results of research on the most important demographic parameters with regard to magnate family's establishment, development and dissolution (among others, both spouses' age at marriage, marriage duration, a number of children in a family and their age at death as adults). Nevertheless, even though listing basic de mographic parameters is vital in itself, due to the importance of comparative studies, they acquire a greater value if we compare the obtained results with those calculated for the then social elites in West European countries. For this reason, another crucial aspect of the work is a comparison of a demographic state of Lithuanian magnates and West European elites. I have also intended to show the process of establishment and dissolution of a magnate family as well as the issue of definitive celibacy among magnate families' representatives, which is a significant problem in the West European research. [From the publication]