Religious studies devote considerable attention to the research of doctrinal influences on social behavior and everyday practices among followers of various religious movements. This study analyzes the demographic behavior of the postniks (one of the “old Russian sectarian” movements) in the Tambov region of the early twentieth century. The paper relies on the relational database developed by the authors during this research. The systematization of archival statistical data and other sources allows the authors to take a closer look at the postniks’ religious life. The population pyramid based on the available data indicates their deep distinction from “ordinary” Orthodox peasants of the Tambov province. The same significant differences exist in the number of children in a family and other compared indicators. The authors argue that this specific demographic behavior is a consequence of the worldview attitudes of the postniks rather than any external factors.