Studies concerning the dynamics of party systems between parliamentary elections are usually based on legislative party switching analyses. This issue was considered and proved in some Western European case studies as well as in some comparative analyses dedicated to the parliaments in the consolidated democracies. But the personal structures of the parliaments in the East-Central European countries are impacted by more than just party switching processes. In this article we propose adopting a broader concept of intraparliamentary volatility, which includes both party switching and replacements of parliamentary mandates. Using data from a full term, 2011–2015, we reconstructed chronological changes in the personal structure of the lower house of the Polish parliament, placing them on a specially created timeline with the intervals marked for each month and distinguishing between change resulted from party switching and replacement of parliamentary mandate. During the period we analyzed the number of independent deputies and the number of parties in the parliament increase alongside with the approaching of the next election. We claim this indicates a stable level of intraparliamentary volatility – immanent for the party systems between parliamentary elections – but this could rise when some special occurrences (i.e. other types of elections or splits within the relevant political party) take place.