This review highlights the urgency for a seamless and co-ordinated approach to service delivery for people with intellectual disability and mental illness. There is emerging evidence of the high prevalence of mental illness in persons with intellectual disability. The notion that people with intellectual disability can have mental illness has only been recently acknowledged. Furthermore, people with intellectual disability also experience a wide range of psychiatric disorders often seen in the general population. Despite of recent developments in treatment options for these people, many of them continue to experience barriers in accessing mental health services.