Background: Accumulating evidence internationally points to an increased risk of crime perpetration and victimization among people with an intellectual disability (ID). This study aimed to examine the impact that comorbid mental illness had on the association between intellectual disability, crime perpetration and criminal victimization. Method: A case linkage methodology involving 2,220 individuals with an intellectual disability from an Australian State. Results: One in four (27%) had contacts with public mental health services; 8.2% had a comorbid mental illness. This "dual disability" group was between 2.97 and 3.22 times more likely than those with intellectual disability alone to have a history of criminal charges, and between 2.76 and 2.97 times more likely to have been a victim of crime. Conclusions: The extent of criminality and victimization found among people with dual disability indicates a potentially multiply stigmatized group for whom the need for a coordinated cross-agency service response remains paramount.