This article investigates the link between state decentralization and party decentralization. We study the impact of the type (dual, integrative, asymmetrical) and degree of decentralization on two dimensions of the relationship between a party’s central party organs and its regional branches: the autonomy of the regional branches to manage their regional affairs and the degree of participation of the regional branches in the central party. We compare the organization of five state-wide parties in two decentralized multi-national polities, Spain and the UK. Our analysis of their party statutes partly confirms the link between degree and asymmetry of decentralization and party organization. However, the impact of the type of distribution of powers between the state and its regions is much less clear. This article shows the need to investigate the influence of other factors such as regional party competition and electoral rules on the type of central-regional relationships within state-wide parties.