Researchers and clinicians have generally agreed that persons with autism spectrum disorders (ASD) are susceptible to other DSM Axis I disorders. However, to date, little has been done to establish the specific disorders, their rate and severity of occurrence, and their interrelationship with ASD symptoms. One reason for the lack of research has been the absence of a comorbidity measure for this population. Additionally, when research has been conducted, it typically has been on one disorder with young children. The present study assessed comorbid DSM Axis I disorders in adults with ASD, either autism or PDDNOS and intellectual disabilities, using a new scale designed for the purpose. The reliability and factor structure of the scale was evaluated and implications for future research are discussed.