This article examines the impact of cognitive ability on ideological voting. We find, using a U.S. sample and a Danish sample, that the effect of cognitive ability rivals the effect of the traditionally strongest predictor of ideological voting, political sophistication. Furthermore, the results are consistent with the effect of cognitive ability being partly mediated by political sophistication. Much of the effect of cognitive ability remains, however, and is not explained by differences in education or openness to experience either. The implications of these results for democratic theory are discussed.