The only beneficial agent for the treatment of chronic delta hepatitis (CDH) is interferon (IFN). However, there is no consensus on the best dosage or duration of IFN therapy. As ribavirin (RBV) increases the sustained response when added to IFN in chronic hepatitis C, probably because of its immunomodulatory effect, we aimed to investigate the efficacy of 2-year IFN treatment and whether RBV had any additive effect to IFN in CDH. Methods: Patients (n=31) with CDH were randomized with a 1:2 ratio as 10 patients (3 females/7 males, age 39 +/- 9) receiving IFN monotherapy (9 MU IFN-alpha 2a three times weekly) and 21 patients (8 females/13 males, age 38 +/- 11) receiving IFN plus RBV for 2 years (IFN at the same dosage and RBV at 1000-1200 mg/day). Alanine transferase normalization and hepatitis delta virus (HDV) RNA negativity at the end of treatment and at the end of the follow-up period (at least 6 months following 2-year treatment) were primary endpoints of the study. In addition, virological response and biochemical response were determined separately.