Although intolerance of uncertainty (IU) has been proposed as a transdiagnostic feature of anxiety, there has been little consensus on its definition and its subcomponents – especially in youth. We report on the development and initial validation of the Youth Intolerance of Uncertainty – Parent-report (YIU-PR), a developmentally sensitive, parent-report measure of IU. Also, we explored age as a possible moderator of the relationship between YIU-PR and symptoms of obsessive-compulsive disorder and anxiety disorders. Caregivers (N = 731, 61.7% female, 73.2% non-Hispanic White) with children between 6 and 17 years old were recruited via Amazon Mechanical Turk and reported on their child’s IU and anxiety. An exploratory factor analysis of YIU-PR items yielded 4 subscales: Difficulty Tolerating Waiting Periods (α = 0.90), Doubting and Reassurance Seeking (α = 0.90), Overestimation of Negative Events (α = 0.92), and Physical and Behavioral Responses (α = 0.87). The 26-item YIU-PR demonstrated excellent internal consistency overall (α = 0.96) as well as concurrent and discriminant validity. There was evidence that IU, as measured by the YIU-PR, was distinct from youth anxiety. The YIU-PR significantly predicted separation anxiety, generalized anxiety, social anxiety, and obsessive-compulsive symptoms in the full sample and generalized anxiety and social anxiety in the clinical subsample. Age did not moderate the relationship between the YIU-PR and anxiety symptoms. Results provide preliminary support for the use of the YIU-PR to measure youth intolerance of uncertainty in clinical and nonclinical settings.