Aims: Limited information exists about the prevalence of psychiatric illness for Indigenous Australians. This study examines the prevalence of diagnosed psychiatric disorders in Indigenous Australians and compares this to non-Indigenous Australians. The aims were to: (1) determine prevalence rates for psychiatric diagnoses for Indigenous Australians admitted to hospital; and (2) examine whether the profile of psychiatric diagnoses for Indigenous Australians was different compared with non-Indigenous Australians.

Methods: A birth cohort design was adopted, with the population consisting of 45 141 individuals born in the Australian State of Queensland in 1990 (6.3% Indigenous). Linked administrative data from Queensland Health hospital admissions were used to identify psychiatric diagnoses from age 4/5 to 23/24 years. Crude lifetime prevalence rates of psychiatric diagnoses for Indigenous and non-Indigenous individuals were derived from the hospital admissions data. The cumulative incidence of psychiatric diagnoses was modelled separately for Indigenous and non-Indigenous individuals. Logistic regression was used to model differences between Indigenous and non-Indigenous psychiatric presentations while controlling for sociodemographic characteristics.

Results: There were 2783 (6.2%) individuals in the cohort with a diagnosed psychiatric disorder from a hospital admission. The prevalence of any psychiatric diagnosis at age 23/24 years was 17.2% (491) for Indigenous Australians compared with 5.4% (2292) for non-Indigenous Australians. Indigenous individuals were diagnosed earlier, with overrepresentation in psychiatric illness becoming more pronounced with age. Indigenous individuals were overrepresented in almost all categories of psychiatric disorder and this was most pronounced for substance use disorders (SUDs) (12.2 v. 2.6% of Indigenous and non-Indigenous individuals, respectively). Differences between Indigenous and non-Indigenous Australians in the likelihood of psychiatric disorders were not statistically significant after controlling for sociodemographic characteristics, except for SUDs.

Conclusions: There is significant inequality in psychiatric morbidity between Indigenous and non-Indigenous Australians across most forms of psychiatric illness that is evident from an early age and becomes more pronounced with age. SUDs are particularly prevalent, highlighting the importance of appropriate interventions to prevent and address these problems. Inequalities in mental health may be driven by socioeconomic disadvantage experienced by Indigenous individuals.