Background: Extreme political attitudes have been on the rise since the economic and political crisis of 2008.This surge of extremism constitutes a real threat, as attitudes like these are dangerous for the peaceful, democratic functioning of society.A new cognitive style, Monopoly on Truth has been proposed, based mainly on the concept of naïve realism.Method: The development and validation of a scale for this new construct is the main objective of this study.A pilot study (N=209) was performed in order to gather the items that make up the fi nal scale; and a main study (N=369) was conducted to test the validity and predictive power of the scale.Results: The validation is successful as the scale shows good reliability scores, while also proving to be linked to extremism-related constructs.Additionally, the scale shows signs of not being ideologically biased.Conclusion: Results show the scale to be a very useful tool for studying extremism and other political trends.Future directions and other implications of the Monopoly on Truth are also discussed.