Studies have shown that multiple office-holding, a practice that denotes the simultaneous exercise of any directly elected municipal mandate and parliamentary seat, is more commonplace in European national parliaments than expected. However, research in Belgium, and especially in the Netherlands, is scarce and extremely fragmented. Therefore, our analysis provides a systematic comparison between the Low Countries with a longitudinal focus. In the first part of the paper, the frequency of the practice is described and its evolution in the last two decades tracked. In the second part, we provide aggregated explanations for the identified discrepancy. Indeed, our results show that after the most recent elections, more than 80% of all Belgian members of parliament held a local mandate, and this percentage increased by 10% during our reference period. In contrast, 9 out of 150 members of the Dutch Second Chamber were combining several offices at the beginning of their national mandate, while the degree of cumulards remained stable. Unexpectedly, the legislative framework and the party regulations are not the source of this deviation, as they are almost identical in both countries. We argue that the difference can be attributed to the role and position of the local government, the political culture and the electoral system.