Most parliamentary democracies have seen a rise of populist radical parties during the past decades. Many countries have also experienced severely delayed government formation processes, with caretaker governments in office for extended periods of time. Are these delays related to the rise of radical parties? We argue that the rise of populist radical parties may prolong the bargaining process, due to the fact that these parties are often treated as pariahs by other parties during election campaigns, which creates a complex bargaining situation after the election. We evaluate this claim by studying 121 government formation processes in the German States from 1990 until 2021, using original data which includes statements made by parties during election campaigns. The findings show that a higher share of seats allocated to parties from the radical right and radical left results in an increasing amount of days until a new government is voted into office. We also find that when a party that has been characterized as being ‘non-coalitionable’ during the election campaign ends up among the negotiating parties, the government formation process is severely delayed. These findings suggest that the rise of populist radical parties may create severe challenges for parliamentary democracy.