This article addresses the effects of decentralisation reforms on regionalist parties' electoral strength. It takes up the debate between ‘accommodatists’ (i.e., electoral loss due to policy accommodation) and ‘institutionalists’ (i.e., electoral gain due to institutional empowerment). These effects depend on the electoral venue considered – regional or national – and on the ideological radicalism of a given regionalist party – secessionist or autonomist. This study finds that increases in the level of decentralisation are positively associated with higher scores for autonomist parties in regional elections, while they are not statistically significantly correlated with secessionist parties' electoral performances. In contrast, in national elections, decentralisation reforms seem to penalise autonomist parties more than secessionist ones. These findings are based on the analysis of a novel dataset which includes regional and national vote shares for 77 regionalist parties in 11 Western democracies from 1950 until 2010.