This is an individual National Research Service Award for post-doctoral research training, which provides support for promising Fellowship Applicants with the potential to become productive, independent investigators in scientific health-related research fields. Evidence suggests 30-80% of youth with autism also suffer from clinical anxiety, though diagnostic interviews used to assess anxiety have not been validated in youth with autism spectrum disorders. It is unclear whether the high rates of comorbid anxiety disorders generated by these assessment instruments actually reflect clinical anxiety, or if they reflect a false positive result. It is possible that features of autism are misclassified as anxiety by standard diagnostic interview schedules. On the other hand, the high rates of anxiety disorder diagnoses could reflect widespread clinically impairing anxiety in youth with ASD, which could result in greater functional impairment and a more severe course of the ASD. The goal of this study is to use multiple methods of assessment, including structured behavioral observations and psychophysiological techniques, as well as clinician-, parent-, and youth-report, to test the validity of anxiety diagnoses generated by a widely used diagnostic interview schedule among youth with ASD. One hundred twenty children ages 7-14 years with a diagnosis of an ASD will be included. Additionally, the work will test whether objective indices of anxiety improve corresponding with improvements in clinician, parent, and youth ratings of anxiety over the course of cognitive-behavioral therapy for youth with ASD and comorbid anxiety. This work will contribute to the field by facilitating understanding of the nature and impact of anxiety in autism, thereby aiding in the development of more targeted and effective treatment strategies.