Throughout its 40-year history, the Vlaams Belang (VB, Flemish Interest) has established itself as an important player within the Belgian party system, although it witnessed significant electoral fluctuations. In 2019, it became the second largest party in Flanders. The party developed and maintains a mass party organisation by investing significantly in local party branches and in a rigid vertically articulated structure. It relies heavily on social media, particularly Facebook, to communicate to supporters (beyond the more restricted group of party members). Whether using modern or traditional tools, VB representatives aim to create communities of supporters that are bonded to the party, which in turn facilitates dissemination of the party’s messages. Despite this investment in maintaining a grassroots organisation, the VB’s decision-making remains highly centralised. Formal centralisation may be partly mitigated by the informal consideration of members’ views using social media and local activists’ organisational freedom, but the party has not created significant mechanisms for internal democracy. While it is often claimed that political parties have moved away from the ‘mass party’ model, this article demonstrates that the VB still shows this model’s characteristics. New social media tools facilitate the party’s attempts to reach a broader public, thus helping it to circumvent Belgium’s strict cordon sanitaire.