About one third of people with an intellectual disability have a psychiatric disorder, and 1 out of 50 individuals with a psychiatric illness have an intellectual disability. These individuals are at elevated risk for adverse psychiatric and social outcomes.
The Mental Health and Developmental Disabilities (MHDD) National Training Center, funded by the Administration for Community Living, is a national clearinghouse for information to address the mental health needs of people with developmental disabilities. Access free resources here.
For more information about comorbidity between intellectual disability and psychiatric illness, see this article.