European politicians have become increasingly concerned about the possible distorting effects of citizens not only being uninformed, but systematically misinformed about the European Union (EU). Against this background, this study assesses the role of EU knowledge in shaping the preference to vote to leave or remain in a (hypothetical) referendum on EU membership using cross‐national survey data that were collected simultaneously in eight EU countries during the run‐up to the 2019 EP elections. The surveys included a newly designed item battery of EU knowledge capturing both the accuracy as well as confidence in knowledge of the respondents. The results show that misinformedness is associated with a preference to leave the EU, the uninformed citizens tend to be undecided or not intending to vote, while the well‐informed prefer to remain. Overall, our findings contribute to the ongoing debates about the role of misinformation in politics.