This article examines the meaning of the ‘Flemish Day’ at the Brussels World Exhibition of 1958 for the formation of the Flemish nation. With this one-day festival pro-Flemish organisations contested the francophone character of the Expo, and francophone dominance in Belgian society. Its success announced the steep advance of the Flemish movement in the second half of the twentieth century. But how can we best interpret its impact on Flemish nation-building? The article analyses reactions on the Flemish Day in the Flemish press. Using six newspapers of diverse ideological strands it assesses support for Flemish emancipation. It thereby reveals a broad acceptance of the legitimacy of the Flemish Day, despite remarkable ideological differences. The discourse analysis supports the hypothesis that broadly shared interpretations of, and an almost unanimous identification with Flanders, provided the foundation for the mass spreading of Flemish consciousness in the 1960s and 1970s. Contributing empirical evidence to the study of nation-building in post-war Flanders, this article demonstrates the importance of media as mirrors and sources of national discourses.