Objective The current research aimed to assess the association between country of birth and use of a specialised mental health service in Sydney, Australia. Methods Patient file data were analysed from individuals who accessed the Clinic for Anxiety and Traumatic Stress in Western Sydney between 1996 and 2010. Patients had undergone a clinical assessment and research interview prior to receiving treatment. Data on demographic information and health history were extracted from these files. South East (SE) Asian‐ and Middle Eastern‐born minority groups were compared with an Australian‐born majority group, using country of birth as a proxy measure of ethnicity. Ratios of service use by group were compared with data on ethnicities residing within the local government area health district. Results Relative to the local population, country of birth minority status was associated with fewer patients accessing the service, with SE Asian‐born patients reporting low service use across all cohorts studied. However, Middle Eastern‐born patients' service utilisation increased over time, becoming commensurate with the local population. Middle Eastern‐born patients reported a significantly shorter delay to seek treatment compared with Australian‐born patients, although no significant differences were reported between ethnic minority groups. Conclusions Differences between SE Asian‐ and Middle Eastern‐born groups in service utilisation patterns over time and treatment delay relative to an Australian‐born group highlight the importance of better understanding the impact of ethnicity on service use.