This study was designed to establish the initial psychometric properties of the first scale specifically developed for behavior problems of adults with Autism Spectrum Disorders (ASD) and intellectual disability (ID). The Autism Spectrum Disorders-Behavior Problems for Adults (ASD-BPA) consists of 20 items in which raters indicate if each item is a "problem" or "no problem." One hundred seventy-one adults with ASD and ID from two developmental centers participated. The majority of participants (88%) had profound ID. Inter-rater, test-retest, and internal consistency correlation coefficients were computed. Item and factor analyses were also examined and a four-factor model was chosen including Aggression/Destruction, Stereotypy, Self-Injurious Behavior, and Disruptive Behavior. Reliability was moderate to good, internal consistency was very good, and model fit was good. The ASD-BPA may prove to be a useful tool for future research in delineating aspects of problem behaviors in adults that are associated with ASD symptoms. In addition, this research may also distinguish behaviors associated with ASD versus cormorbid psychopathology and/or ID, thus providing implications for clinical practice. (Contains 5 tables.)