This article explores the relationship between constitutionalism and populism with particular attention paid to the Italian case. This piece is divided into two parts. In Part I it will be argued that the relationship between populism and constitutionalism should not be seen in terms of mutual exclusion and perfect opposition. Indeed, it is possible to say that populism frequently relies on concepts and categories belonging to the language of constitutionalism (majority, democracy, people), trying to reshape them and offering in this way a sort of constitutional counter-narrative. In this sense, the populist approach to constitutional categories can be described in light of two concepts: mimetism and parasitism. In Part II, I shall focus on the referendum, which is an instrument frequently used by populists and currently object of a problematic constitutional reform proposal advanced by the MoVimento 5 Stelle. As we will see this reform risks affecting the constitutional balance between powers in Italy.