Since Lipset and Rokkan (1967) published their seminal work on the importance of social cleavages for the ‘freezing’ of party systems more than forty years ago, much has been written on the field demonstrating or discrediting the original hypothesis. In the current article, I examine how cleavage formation and development have influenced the different levels of institutionalization in four new post-communist party systems (i.e. Visegrad). Analysing distinct hypotheses, I arrive at the conclusion that neither the number nor the type nor the strength of a cleavage is associated with the degree of party system institutionalization in East Central Europe. On the contrary, the main conclusion is that party system institutionalization in these democracies has been determined by the way cleavages are structured. In particular, the process of party system institutionalization is found to be hindered when cleavages cross-cut, while fostered in cases where they cumulate (i.e. coincide).