Symptoms of irritability, anxiety, panic, and insomnia are common in patients with depression, and their worsening after antidepressant treatment initiation is associated with poorer long-term outcomes. The Concise Associated Symptom Tracking (CAST) scale was developed to measure these symptoms in adults with major depressive disorder (MDD). Here, we evaluate the psychometric properties of CAST in an ongoing community-based observational study involving children, adolescents, and young adults. Individuals from the ongoing Texas Youth Depression and Suicide Research Network (TX-YDSRN; N = 952) with CAST data available were included. Fit statistics [Goodness of Fit Index (GFI), Comparative Fit Index (CFI), and Root Mean Square Error of Approximation (RMSEA)] from confirmatory factor analyses were used to evaluate the five- and four-domain structure of CAST. Item response theory (IRT) analyses were also used. Individuals were grouped based on age (in years) as youths (8-17) and young adults (18-20). Correlations with other clinical measures were used to inform construct validity. Four-domain (irritability, anxiety, panic, and insomnia) 12-item structure of CAST (CAST-12) was optimal for youths (N = 709, GFI = 0.906, CFI = 0.919, RMSEA = 0.095) and young adults (N = 243, GFI = 0.921, CFI = 0.938, RMSEA = 0.0797) with Cronbach's alpha of 0.87 and 0.88, respectively. Slope of each item exceeded 1.0 on IRT analyses suggesting adequate discrimination for each item. Scores on irritability, anxiety, panic, and insomnia were significantly correlated with similar items on other scales. Together these findings suggest that CAST-12 is a valid self-report measure of irritability, anxiety, insomnia, and panic in youths and young adults., Competing Interests: Declaration of competing interest Dr. Jha has received contract research grants from Acadia Pharmaceuticals, Neurocrine Bioscience, Navitor/Supernus and Janssen Research & Development, educational grant to serve as Section Editor of the Psychiatry & Behavioral Health Learning Network, consultant fees from Eleusis Therapeutics US, Inc, Janssen Global Services, Janssen Scientific Affairs, Worldwide Clinical Trials/Eliem and Inversargo, and Guidepoint Global, and honoraria from North American Center for Continuing Medical Education, Medscape/WebMD, Clinical Care Options, and Global Medical Education. Dr. Blader reports having received consultant and speakers' honoraria from Supernus Pharmaceuticals. Dr. Brown has received consulting fees from Sage and Biogen Pharmaceuticals. Dr. Kennard receives royalties from Guilford, Press, Inc; and serves on the board of trustees for the Jerry M. Lewis, III, MD Research Foundation. Dr. Soutullo reports for the period 2018–2022 non-personal research funds from Lundbeck and Janssen; is a consultant/advisory board member of Editorial Médica Panamericana, EUNETHYDIS (European Network on Hyperkinetic Disorder), NeuroTech Solutions Ltd (Israel), Limbix Health DSMB (United States), MEDEA (Spain), Tech Innosphere Engineering LTD (Germany), and Shire/now part of Takeda (Spain); received speaker's bureau fees from Bial (Portugal), Cuquerella Medical Consulting (Spain), Medice (Germany), Rubio (Spain), Tecnofarma (Peru), and Shire/now part of Takeda (Spain), and royalties from Editorial Médica Panamericana (Spain). Dr. Storch reports receiving research funding to his institution from the Ream Foundation, International OCD Foundation, and NIH. He is a consultant for Brainsway and Biohaven Pharmaceuticals. He owns stock less than $5000 in NView. He receives book royalties from Elsevier, Wiley, Oxford, American Psychological Association, Guildford, Springer, and Jessica Kingsley. Dr. Trivedi has provided consulting services to Alkermes Inc, Axsome Therapeutics, Biogen MA Inc., Cerebral Inc., Circular Genomics Inc, Compass Pathfinder Limited, GH Research Limited, Heading Health Inc, Janssen, Legion Health Inc, Merck Sharp & Dohme Corp., Mind Medicine (MindMed) Inc, Merck Sharp & Dhome LLC, Naki Health, Ltd., Neurocrine Biosciences Inc, Noema Pharma AG, Orexo US Inc, Otsuka American Pharmaceutical Inc, Otsuka Canada Pharmaceutical Inc, Otsuka Pharmaceutical Development & Commercialization Inc, Praxis Precision Medicines Inc, SAGE Therapeutics, Sparian Biosciences Inc, Takeda Pharmaceutical Company Ltd, WebMD. He sits on the Scientific Advisory Board of Alto Neuroscience Inc, Cerebral Inc., Compass Pathfinder Limited, Heading Health, GreenLight VitalSign6 Inc, Legion Health Inc, Merck Sharp & Dohme Corp, Orexo US Inc, Signant Health. He holds stock in Alto Neuroscience Inc, Cerebral Inc, Circular Genomics Inc, GreenLight VitalSign6 Inc, Legion Health Inc. Additionally, he has received editorial compensation from American Psychiatric Association, and Oxford University Press. Drs. Minhajuddin, Slater, Garza, Shotwell, Wakefield, and Mrs. Mayes have no declarations to report., (Copyright © 2023. Published by Elsevier Ltd.)