Hepatitis C viral (HCV) infection is present in 30 to 98% of intravenous drug users. Intravenous substance abuse represents the main route of HCV transmission in industrialized countries. A multi-centre, randomized, controlled, prospective study assessed sustained virological response (SVR), adverse events such as depressive episodes and retention rate of HCV treatment in opioid-dependent patients. Stabilized, opioid-dependent patients with chronic HCV infection (genotype 2 or 3) received pegylated interferon alpha-2a in combination with ribavirin 800 mg/day (Group A) or 400 mg/day (Group B). Participants were randomized, blocked and stratified by genotype and viral load. A standardized psychiatric assessment, Beck Depression Inventory (BDI) and Van Zerssen's list of complaints were administered at each study visit. In 31 months, 300 opioid-dependent patients were screened; 190 (63.3%) were hepatitis C antibody positive. According to study protocol, out of 75 'potential-to-treat' patients with genotype 2 or 3, 17 stable patients (22.6%) were included in the study. All participants completed the study. Significant haemoglobin decreases occurred in both Groups A (P = 0.001) and B (P = 0.011). All the patients had an end-of-treatment (week 24) HCV RNA negativity. Fifteen (88.2%) achieved SVR at week 48. Overall, 52.9% developed depressive symptoms during treatment. Because of the prompt initiation of antidepressant medication at first appearance of depressive symptoms, no severe depressive episodes occurred. Our data show a high retention rate and reliability, and good viral response for both treatments. Hepatitis C treatment in stable opioid-dependent patients was efficacious, suggesting that addiction clinics can offer antiviral therapy in combination with agonistic treatment as part of multi-disciplinary treatment.