The paper discusses the changes in the population of the world's smallest countries during the 20th century. It includes four research questions, four hypotheses concerning the changes in the population and their consistency with the demographic transformation model, verification of the demographic features associated with such countries, typology of population changes and factors underlying population change in the microstates. 32 of 34 microstates identified in a formalised way have been analysed. To verify the hypotheses, the authoress employs an analysis based on the Geddes rate of variation, standard variation of demographic rates, typological procedure and analysis of factors underlying population change based on the frequency of occurrence of individual types of factors.