Children and adolescents with intellectual and developmental disabilities (IDD) experience higher rates of psychopathology and problem behavior compared to typically developing children (de Ruiter, Dekker, Verhulst, & Koot, 2007; Einfeld, Ellis, & Emerson, 2011). Clinical practice and research depend on being able to adequately describe and quantify these constructs. While there are several well-established tools to measure psychopathology and problem behavior in a typically developing population, only a few have been developed for children and adolescents with IDD. One of these tools is the Nisonger Child Behavior Rating Form (NCBRF; Aman, Tasse, Rojahn, & Hammer, 1996; Tasse, Aman, Hammer, & Rojahn, 1996), which is a popular rating scale among the limited number of assessments developed for children and adolescents with IDD. Psychometric research on the NCBRF has indicated that the factor structure may not perform as well as it was shown to in the original normative sample (Lecavalier, Aman, Hammer, Stoica, & Matthews, 2004; Norris & Lecavallier, 2011; Rojahn et al., 2010). The current study aimed to update the NCBRF to increase the clinical applicability and improve the psychometric properties. To increase clinical applicability, the updated NCBRF was aligned with current theory on prevalent childhood psychopathology according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association, 2013). The most prevalent disorders in children and adolescents with IDD include attention-deficit/hyperactivity disorder (ADHD), anxiety disorder, depressive disorders, oppositional defiant disorder, and conduct disorder (Dekker & Koot, 2003; Emerson & Hatton, 2007; Strømme & Diseth, 2000). In addition to these four diagnostic categories, self-injury and aggression are commonly seen in this population (Kanne & Mazurek, 2011; MacLean, Tervo, Hoch, Tervo, & Symons, 2010; McClintock, Hall, & Oliver, 2003). To align items and subscales with these psychopathology and problem behavior categories, an expert panel process using the Delphi method was employed. Upon completion of the expert panel review, new items were gathered to form the updated version of the NCBRF (NCBRF-2). This updated version was completed by 401 parents or caregivers of children ages 3 to 18 who were seen for an interdisciplinary developmental assessment or a comprehensive psychological evaluation at Nationwide Children’s Hospital’s Child Development Center. The sample was predominantly children diagnosed with autism spectrum disorder. Confirmatory factor analysis was used to test the theory-driven model of the NCBRF-2. The factor structure showed good fit and internal consistency. Subscales were compared with regards to sex and chronological age. While no differences were observed with regards to sex. Chronological age, as expected, showed several differences among the NCBRF-2 subscales. Normative data are presented for chronological age divided into four groups (i.e., children 3 and 4, children 5 and 6, children 7 to 10, and children 11 to 18 years old). Finally, concurrent and discriminant validity were tested by correlating the NCBRF-2 subscales with other child behavior rating measures and results supported emerging validity evidence. The NCBRF-2 has improved clinical applicability and psychometric properties compared to the original version and adds to the field of clinical practice and research for children and adolescents with IDD.