Anxiety disorders are common among children but can be difficult to diagnose. An actuarial approach to the diagnosis of anxiety may improve the efficiency and accuracy of the process. The objectives of this study were to determine the clinical utility of the Achenbach Child Behavior Checklist (CBCL) and Youth Self Report (YSR), two widely used assessment tools, for diagnosing anxiety disorders in youth and to aid clinicians in incorporating scale scores into an actuarial approach to diagnosis through a clinical vignette. Demographically diverse youth, 5 to 18 years of age, were drawn from two samples; one (N = 1,084) was recruited from a research center, and the second (N = 651) was recruited from an urban community mental health center. Consensus diagnoses integrated information from semistructured interview, family history, treatment history, and clinical judgment. The CBCL and YSR internalizing problems T scores discriminated cases with any anxiety disorder or with generalized anxiety disorder from all other diagnoses in both samples (ps < .0005); the two scales had equivalent discriminative validity (ps > .05 for tests of difference). No other scales, nor any combination of scales, significantly improved on the performance of the Internalizing scale. In the highest risk group, Internalizing scores greater than 69 (CBCL) or greater than 63 (YSR) resulted in a Diagnostic Likelihood Ratio of 1.5; low scores reduced the likelihood of anxiety disorders by a factor of 4. Combined with other risk factor information in an actuarial approach to assessment and diagnosis, the CBCL and YSR Internalizing scales provide valuable information about whether a youth is likely suffering from an anxiety disorder.