A considerable number of patients undergoing methadone maintenance treatment (MMT) are not considered for treatment against hepatitis C virus (HCV) infection due to a possible lower adherence and efficacy in this population. We aimed to compare the response rates to HCV treatment in patients with or without MMT. HCV-infected patients who initiated pegylated interferon plus ribavirin were included in this prospective cohort study. The relation between sustained virologic response (SVR) and MMT was analyzed. A total of 214 patients were included in the study [81 (37.9%) with and 133 (62.1%) without MMT]. No differences in HCV and interleukin 28B (rs12979860) genotype distribution were observed between the two groups. Of these patients, 103 (48.1%) achieved SVR. Among the patients who received MMT, 39 (48.1%) reached SVR compared to 64 (48.1%) subjects without MMT (p = 0.99). The frequency of voluntary drop-out and treatment discontinuations due to adverse events was comparable between the patients with and without MMT [10 (12.3%) versus 14 (10.5%), p = 0.68, and 4 (4.9%) versus 9 (6.8%), p = 0.59, respectively]. The efficacy of HCV therapy in MMT patients is similar to that found in subjects not taking methadone. MMT patients should be equally considered for treatment with pegylated interferon plus ribavirin in HCV-infected patients.