Cognitive theory conceptualizes worry as influenced by metacognitive beliefs about worry, intolerance of uncertainty, and perceptions of control over events and reactions. This study tests the hypothesis that the effect of intolerance of uncertainty would interact with meta-cognitive beliefs on worry and perceived control. One hundred eighteen individuals with generalized anxiety disorder and 54 controls completed the Meta-Cognition Questionnaire, the Intolerance of Uncertainty Scale, the Anxiety Control Scale, and the Penn State Worry Questionnaire. Models were tested measuring interactive effects in multiple regression linear analysis. The interaction model was confirmed. The effect of intolerance of uncertainty on worry was increased by its interaction with metacognitive and control beliefs. The finding emphasizes the significant role of metacognitive and control beliefs in the cognitive process that leads to the development of worry.