OBJECTIVE:There are good data regarding the prevalence and patterns of dual diagnosis among the general population; however, data regarding the older adult cohort are limited. We aimed to extend the knowledge of the point prevalence and patterns of dual diagnosis among older adults and the impact of dual diagnosis on the utilization of alcohol and other drug treatment services. METHOD:A 12-month medical chart audit of clients discharged from an Australian older adult-specific alcohol and other drug treatment service was performed. Measures included the Alcohol Use Disorders Identification Test-Consumption, the Drug Use Disorders Identification Test-Consumption, the Kessler 10, and the Modified MINI Screen. Additional data collected included mental health diagnoses, number of session types, and treatment outcomes. RESULTS:There were 79 (n = 45, 57% male) medical charts audited, with a mean age of 65.9 years (SD = 5.8). There were 68 (89%) clients having at least one comorbid mental illness. Clients with a dual diagnosis were younger (p = .011) than those without. Some comorbid mental health conditions were associated with additional service utilization (p < .05). Clients with personality disorders required more telephone calls and outreach services (p < .05). The number of mental health diagnoses was associated with additional treatment sessions (p < .05). CONCLUSIONS:Further research with a larger sample size of older adults seeking age-specific alcohol and other drug treatment services is required. Older adult-specific alcohol and other drug treatment services need to allow for longer episodes of care for clients with certain dual diagnoses and a focus on reducing anxiety to increase treatment retention.