The current study examined the association between changes in intolerance of uncertainty (IU) and treatment outcomes for anxious youth. Participants were youth ages 7 to 17 who received cognitive behavioral therapy for anxiety (N = 73). Youth and their primary caregivers completed a diagnostic interview and self- and parent-report measures at pre- and post-treatment, including the Intolerance of Uncertainty Scale for Children (IUS-C/P; Przeworski, 2006), the Coping Questionnaire (CQ-C/P; Kendall, 1994) and the Multidimensional Anxiety Scale for Children (MASC-C/P; March et al., 1997). Hierarchical regression analyses evaluated the role of change in IU (the IUS-C/P) in predicting changes in functional impairment, coping efficacy, and anxiety severity post-treatment, controlling for demographic variables (age and gender), and baseline levels of IU, anxiety severity, functional impairment, and coping efficacy. Results demonstrated that treatment was associated with improvements across child-, parent- and clinician-report, and decreased IU from pre- to post-treatment was associated with (a) decreased functional impairment, (b) increased coping efficacy and (c) decreased anxiety severity. The findings indicate that a greater reduction in IU over treatment is associated with better outcomes in children and adolescents with anxiety across informants, suggesting the possibility that an increased focus on IU during treatment for youth anxiety may improve treatment outcomes. Future research should assess the causality of this relationship.