Uptake of treatment for hepatitis C virus (HCV) infection is very low particularly among people who have injected drugs. Opiate substitution treatment (OST) programs, with a high prevalence of people living with HCV, have been a site of growing interest in the delivery of hepatitis C treatment. There has been no exploration of OST clients' and health professionals' perceptions of the barriers and facilitators to uptake and delivery of HCV treatment in OST clinics from personal and organizational perspectives. This qualitative study involved interviews with 27 OST clients in New South Wales and a focus group and interviews with 22 Australian OST health professionals. Clients and health professionals viewed hepatitis C treatment in OST as a 'one-stop-shop' model which could increase access to and uptake of treatment and build on existing relationships of trust between OST client and health professional. Elements of the organizational culture were also noted as barriers to HCV treatment delivery including concerns about confidentiality, lack of discussion of HCV treatment and that HCV treatment was not perceived by clinicians as a legitimate activity of OST clinics. OST client participants also reported a number of personal barriers to engaging with HCV treatment including family responsibilities (and concerns about treatment side effects), unstable housing, comorbidities and perceptions of the unsatisfactory level of treatment efficacy. These findings emphasize the need for future research and delivery of services which addresses the complexity of care and treatment for people in marginalized social circumstances.