Background/Aims Treatment of chronic hepatitis C with interferon can be ineffective due to relapse. We aimed to reduce the 40% relapse rate of 6 months interferon-ribavirin combination therapy by prolonging treatment to 18 months. Methods Three hundred patients with treatment-naive hepatitis C, were randomized to 18 months combination therapy with interferon (3MU tiw) and ribavirin (1000-1200 mg/day), 18 months interferon combined with placebo, or 6 months combination therapy with interferon and ribavirin, in a double blinded manner. All 295 patients who received at least one dose of treatment were included in the intention to treat analysis. Results At the end of treatment, HCV RNA was undetectable in 55 and 49% of those on 6 and 18 months combination therapy, respectively, versus 26% of those on monotherapy (P