The specific relationship of intolerance of uncertainty (IU) to generalized anxiety disorder (GAD) in youth was examined by evaluating the ability of the Intolerance of Uncertainty Scale for Children (IUSC) to discriminate among principal anxiety disorder diagnoses. Analyses examined parent, child, and composite reports of principal anxiety diagnoses in youth aged 7 to 17 years. Results indicate that higher IU scores are associated with GAD by the composite diagnostic. Additionally, the IUSC significantly predicted child-reported anxiety severity. This relationship was not moderated by diagnostic group. The results indicate that IUSC scores are particularly associated with GAD, as well as with more severe child-reported anxiety symptoms.