This four-year multisite project will advance outcome measurement of anxiety in future clinical trials in youth with autism spectrum disorders (ASD). There is a current dearth of outcome measures in developmentally disabled populations—a major impediment for drug research. Impairing anxiety is common in youth with ASD and a potential treatment target. While there exist several well-accepted outcome measures for anxiety in typically developing youth, these measures are not suitable for many individuals with ASD given their language and cognitive deficits. Researchers in this study will therefore develop a parent-rated and a clinician-rated instrument for measuring anxiety in youth with ASD who participate in clinical trials. Investigators propose a mixed method approach that will explore the manifestations of anxiety in children with ASD and use this information to refine existing scales of anxiety.