There have been few studies of psychopathology in adults with autism. This study examined psychiatric co-morbidity in 147 adults with intellectual disability (ID) and autism and 605 adults with ID but without autism. After controlling for the effects of gender, age, psychotropic medication and level of ID, people with autism and ID were no more likely to receive a psychiatric diagnosis than people with ID only. People with autism were less likely to receive a diagnosis of personality disorder. These findings cast doubts on the hypothesis that adults with ID and autism are more vulnerable to certain psychiatric disorders than non-autistic adults with ID.