We evaluated the ability of the Revised Children?s Manifest Anxiety Scale (RCMAS), the State?Trait Anxiety Inventory for Children (STAIC), and the Child Behavior Checklist (CBCL) to (a) discriminate between youth with an anxiety disorder and youth without a disorder, (b) discriminate between youth with an anxiety disorder and youth with either externalizing disorders or affective disorders, and (c) measure treatment change. In addition, variables, including age and sex, were explored as possible moderators of instrument utility. A meta-analysis of 43 articles was conducted. A large effect size was found when the instruments were used to compare youth with an anxiety disorder to youth without a disorder. When comparing anxious youth to psychiatric control groups, the picture was mixed; the instruments were found to be useful when discriminating between youth with an anxiety disorder and youth with an externalizing disorder, but not between youth with an anxiety disorder and children and adolescents with an affective disorder. The RCMAS, STAIC, and CBCL were found to be moderately sensitive to treatment gains.