Autism spectrum disorders (ASD) and intellectual disabilities (ID) are high prevalence developmental disabilities that co-occur at high rates. Furthermore, Axis I psychopathology is known to occur more frequently in individuals with ID than the general population. The problems are lifelong and can be major impediments to independent living. Despite this, little research with adults is available to determine the effects of these disabilities on specific adaptive skills. In this study, 337 adults were evaluated using the Vineland Adaptive Behavior Scale to assess the effects of these disabilities on looking at an ID, ID plus ASD, and ID and ASD plus Axis I psychopathology group. Adaptive skills were greatest for the ID group followed by the ID plus ASD, and ID and ASD plus psychopathology. Thus, the more handicapping conditions, the greater the skills deficits observed, particularly where psychopathology was concerned. As such, accurately identifying the causes of adaptive skill deficits will likely result in more precise and effective treatment. (Contains 3 figures and 3 tables.)