Delayed treatment seeking for people experiencing symptoms of mental illness is common despite available mental healthcare. Poor outcomes are associated with untreated mental illness and caregivers may eventually need to seek help on the service user's behalf. More attention has recently focused on the role of stigma in delayed treatment seeking. This study aimed to establish the frequency of stigma- and non-stigma-related treatment barriers reported by 202 service users and 80 caregivers; to compare treatment barriers reported by service users and caregivers; and to investigate demographic predictors of reporting stigma-related treatment barriers. The profile of treatment barriers differed between service users and caregivers. Service users were more likely to report stigma-related treatment barriers than caregivers across all stigma-related items. Service users who were female, had a diagnosis of schizophrenia or with GCSEs (UK qualifications usually obtained at age 16) were significantly more likely to report stigma-related treatment barriers. Caregivers who were female or of Black ethnicities were significantly more likely to report stigma-related treatment barriers. Multifaceted approaches are needed to reduce barriers to treatment seeking for both service users and caregivers, with anti-stigma interventions being of particular importance for the former group.