Cognitive impairment is one factor known to affect people's ability to participate in substance misuse treatment because of the range of cognitive, behavioural and emotional problems such impairment can cause. Some of the behaviours described as common features of cognitive impairment, such as impaired self-monitoring and self-regulation and lack of initiative are seen in some treatment modalities to be causes and consequences of addiction thereby prescribing a moral rationale to behaviour that may have a physical cause. The aim of this study was to identify the prevalence of cognitive impairment in a rural Australian substance treatment in-patient population. The Addenbrook's Cognitive Examination-Revised (ACE-R) was used to screen consenting patients (n=50). Six (12%) scores were less than or equal to 82 (moderate to severe cognitive impairment), and 20 (40%) were less than or equal to 88 (mild to moderate cognitive impairment). Statistical techniques were used to determine if cognitive impairment was related to different demographic variables. The tests showed that cognitive impairment was not related to age or gender, weakly related to level of education and strongly related to Indigenous status. For example, 82% of Indigenous clients had a score indicating possible impairment, compared to 28% for non-Indigenous. A significant number of people attending in-patient drug and alcohol treatment have some form of cognitive impairment that may affect their ability to participate in the treatment. Indigenous people in rural substance treatment services appear highly likely to have some cognitive impairment. However, further work is required to ensure the screening tool is appropriate for use with Indigenous Australians. Substance misuse treatment providers need to ensure treatment programmes are suitable for people with cognition problems. © 2012 Copyright Taylor and Francis Group, LLC.