The paper investigates whether self-report and performance measures of executive control yield comparable results. We report an empirical study in which the answers to a self-report questionnaire on executive control were compared with the results of three computerized tests of cognitive control. Both the questionnaire and the computerized tests covered three dimensions of executive control, namely, prepotent response inhibition, task switching, and goal monitoring (goal maintenance). The results are rather surprising and negative: The relationships between performance and self-report measures of executive control were either weak or insignificant. Moreover, they tended to disappear when age of participants was controlled. We conclude that people are basically unable to assess the strength of their own cognitive control. However, the two types of assessment tool might analyze different aspects of individual differences in executive control and should therefore be considered in research and practical applications.