ObjectivesTo investigate mortality and its causes in adults over the age of 20 years with intellectual disability (ID).Design, setting and participantsRetrospective population-based standardised mortality of the ID and Comparison cohorts. The ID cohort comprised 42 204 individuals who registered for disability services with ID as a primary or secondary diagnosis from 2005 to 2011 in New South Wales (NSW). The Comparison cohort was obtained from published deaths in NSW from the Australian Bureau of Statistics (ABS) from 2005 to 2011.Main outcome measuresWe measured and compared Age Standardised Mortality Rate (ASMR), Comparative Mortality Figure (CMF), years of productive life lost (YPLL) and proportion of deaths with potentially avoidable causes in an ID cohort with an NSW general population cohort.ResultsThere were 19 362 adults in the ID cohort which experienced 732 (4%) deaths at a median age of 54 years. Age Standardised Mortality Rates increased with age for both cohorts. Overall comparative mortality figure was 1.3, but was substantially higher for the 20–44 (4.0) and 45–64 (2.3) age groups. YPLL was 137/1000 people in the ID cohort and 49 in the comparison cohort. Cause of death in ID cohort was dominated by respiratory, circulatory, neoplasm and nervous system. After recoding deaths previously attributed to the aetiology of the disability, 38% of deaths in the ID cohort and 17% in the comparison cohort were potentially avoidable.ConclusionsAdults with ID experience premature mortality and over-representation of potentially avoidable deaths. A national system of reporting of deaths in adults with ID is required. Inclusion in health policy and services development and in health promotion programmes is urgently required to address premature deaths and health inequalities for adults with ID.

Recommendations are made for adopting a human rights-based approach towards the development and provision of mental health services for people with ID. These include improved policy with measurable outcomes, improved service access via clear referral pathways and the sharing of resources across disability and mental health services, and improved service delivery through training and education initiatives for both the mental health and disability workforce.

Ambulatory mental health data from NSW indicates that people with an ID receive care for a distinct range of mental disorders, and experience uncertainty regarding their diagnosis. People with an ID have higher service needs which require recognition and the allocation of specific resources. Such data provide a suitable baseline for future evaluation of the impact of ambulatory mental health reforms for people with an ID.