Evidence-based treatment must begin with the systematic and comprehensive identification of an individual’s complete clinical picture. Therefore, screening individuals with intellectual disability (ID) for comorbid disorders is imperative. Because of the frequent overlap between autism spectrum disorder (ASD) and ID, the current study explored the effects of co-occurring ASD on the comorbid symptoms exhibited by adults with ID. The study included 307 adults with severe or profound ID separated into two groups: ASD+ID and ID only. The ASD+ID group exhibited significantly more symptomology on eight of the 12 subscales examined including anxiety, mania, schizophrenia, stereotypies/tics, self-injurious behavior, eating disorders, sexual disorders, and impulse control. Further, comparisons of specific symptom endorsements yielded distinct results.