Objective: The Ontario Addiction Treatment Centres (OATC) operates 26 clinics offering methadone maintenance treatment (MMT) to clients with a dependence on opiates. Until recently, MMT was a contraindication to antiviral therapy for the treatment of Hepatitis C virus (HCV) infected patients. The purpose of this study was 1) to describe a care model for treating HCV infected MMT clients in a community-based setting, 2) to describe clinical and demographic characteristics of these clients, 3) to assess rates of adherence to antiviral therapy, and 4) to assess rates of sustained virological response (SVR). Methods: A review of patient medical records was employed. Clients considered for antiviral therapy at the OATC had achieved “functional stability”, characterized by stable housing and a low frequency of substance abuse, in addition to meeting clinical criteria. Clients were followed by a hepatitis nurse, clinic physician or infectious disease specialist at the clinic where they received methadone. Use of illicit substances was monitored before, during and after antiviral therapy with regular urinalysis. Results: Between November 2002 and January 2006, 109 clients (75 with genotype 1/4 and 33 with genotype 2/3) received at least one injection with pegylated interferon. The majority of clients were single (60%), living in a permanent apartment or house (94%), with a high frequency of self-reported psychiatric disorders (68%). A large proportion had a criminal history (71%) and many had been incarcerated (52%). Rates of adherence to treatment of 57% and 70% were achieved for genotypes 1/4, and 2/3, respectively. Rates of SVR in an intention to treat analysis were 51% for genotypes 1/4 and 64% for genotypes 2/3. Six clients discontinued therapy due to on-going problems with substance abuse. Conclusion: HCV antiviral therapy for current or former substance abusers can be successful in the context of specialized care for substance abuse.