Anxiety disorders are the most prevalent disorders among youth and understanding cognitive vulnerabilities for these disorders is crucial for early prevention and treatment. The present study examined the role of intolerance of uncertainty (IU) in predicting the severity of anxiety disorder symptoms among a sample of Iranian youth. The relationships between IU and anxiety disorder symptoms among youth [N = 683, ages 8-18, M (SD)age= 14.02 (2.43); 58.07 % girls] with and without anxiety disorders, and their parents [N = 676, ages 27-58, M (SD)age= 40.63 (5.72); 61.8% female], were examined. Significant associations were found between youth- and parent-report IU and youth anxiety disorder symptoms. Youth with higher scores on total IU and prospective/inhibitory IU dimensions had significantly higher levels of anxiety disorder symptoms. Furthermore, youth-reported prospective/inhibitory IU were significantly related to specific youth anxiety and related disorder symptoms including generalized anxiety, separation anxiety, physical injury fears, obsessive-compulsive, social anxiety and panic/agoraphobia disorder symptoms. Findings provide cross-sectional support for the role of IU as a transdiagnostic feature in predicting a wide range of anxiety disorder symptoms in youth. Implications for future clinical applications are discussed.