Objective: We sought to develop a brief, easy to use behavior checklist to address common limitations in the use of ADHD rating scales in busy clinical settings. Method: Items for the CHAOS (Conduct-Hyperactive-Attention Problem-Oppositional Symptom) scale were developed based on the ratings of Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) criteria provided by experienced clinicians. The scale was administered to mothers of 205 clinically referred children for the purpose of subscale creation based on principal components analysis (PCA). Reliability and validity were analyzed using a separate sample of 139 children referred for psychological testing. Results: PCA resulted in four subscales (Attention Problems, Hyperactivity-Impulsivity, Oppositional Behavior, and Conduct Problems), which demonstrated moderate to high test–retest and interrater reliability. Subscale scores correlated significantly with subscales from a DSM-referenced behavior checklist, along with tests of executive functioning. Conclusion: These data suggest that the CHAOS scale is a brief, psychometrically sound tool for evaluation and monitoring of ADHD symptoms. (J. of Att. Dis. 2013; XX(X) 1-XX)