Individuals with autism spectrum disorder (ASD) are often in need of psychiatric care due to poor emotion regulation and emotional distress. Only two psychotropic medications have been approved for use in ASD, both to treat irritability expressed as tantrums, outbursts, and aggression. However, the underlying deficits in emotion regulation that lead to these problem behaviors are poorly understood and rarely measured or targeted in treatment. Evidence-based treatment approaches for the full range of emotion dysregulation (e.g. depression, outbursts, meltdowns, etc.) present in ASD do not exist. A major barrier to progress in this area is a lack of validated, treatment sensitive measures of emotional distress for individuals with ASD. This project proposes to refine and validate a new measure of emotional distress and emotion regulation for ASD, called the Emotion Dysregulation Inventory (EDI). Guidelines from the Patient-Reported Outcome Measurement Information System (PROMIS) Project and gold-standard statistical approaches will be utilized to complete calibration and psychometric analysis of the EDI. The primary sample will include caregivers of 1000 children and young adults with ASD from community, outpatient, and psychiatric inpatient settings. Data collection will occur through an online system. Analyses will focus on establishing the EDI's factor structure/dimensionality, developing a less than 10-item short form, establishing convergent and divergent validity, comparing EDI scores among groups whose scores would be expected to differ (e.g. inpatients versus community sample; ASD versus healthy controls), and comparing EDI scores to observational counts of emotion dysregulation episodes displayed by children who are inpatients on two specialized psychiatric units. A subset of the sample will complete the EDI twice to establish test-retest reliability. The EDI's ability to detect treatment change will be determined by comparing both caregiver- and provider-rated EDI scores at admission and discharge across two psychiatric inpatient units that specialize in ASD and 4-week change scores in a stable community sample. The primary outcome of this study will be a user-friendly (e.g. available online, brief), validated, treatment sensitive outcome measure for clinical trials in ASD that is independent of verbal ability. In addition, this study will produce he largest existing dataset on emotion dysregulation in ASD, which will be used to identify emotional profiles and treatment needs in this population. Additional time-course questions in the EDI that tap the individual's history of emotion dysregulation will be useful for clinical conceptualization and helping to understand the boundaries between emotion dysregulation that is inherent in ASD and comorbid psychiatric disorders. Finally, having a sensitive measure of emotion dysregulation in ASD will aid in understanding heterogeneity in genetic and neuroimaging research and will enable cross-population studies