The Nisonger Child Behavior Rating Form (NCBRF) was developed to specifically screen psychopathology and problem behavior in children and adolescents with IDD. This study aimed to update the NCBRF to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) and screen for the most prevalent psychopathologies that affect children and adolescents with IDD. The authors re-aligned the existing items to fit within a DSM-5 framework, and then used the Delphi method with a panel of experts in IDD to evaluate the NCBRF items. The revision process included deleting and revising existing items and formulating new items. We obtained a final item pool after three iterations. The Delphi process and resulting item pool are described in this article.