Sweden and Denmark have presented contrasting relationships between centre-right and populist radical right (PRR) parties. In Sweden, the centre-right has refused cooperation with the Sweden Democrats (Sverigedemokraterna) (SD), even when this cost the centre-right office. However, in Denmark, coalitions led by centre-right parties have cooperated with the Danish People’s Party (Dansk Folkeparti) (DF) on multiple occasions. Through a controlled comparison, we examine what explains these different outcomes. Using Chapel Hill Expert Surveys and public opinion data, we firstly look at the policy congruence between parties and the social acceptability of cooperation. We then examine interview material with representatives from centre-right and PRR parties in Sweden and Denmark to see their explanations of cooperation and non-cooperation. We conclude that, while the office goals of Danish centre-right parties, along with the policy focus and uncontroversial past of DF, explain that case, the reputation and past of SD has precluded a similar outcome.