Hepatitis C virus (HCV) induces extrahepatic manifestations such as oral lichen planus (OLP) as well as chronic liver diseases. The treatment of HCV-related chronic liver disease has evolved from the use of a single agent, mainly interferon (IFN), to the combination of IFN and ribavirin. We present a case of erosive OLP, cutaneous lichen planus (CLP), and leukoplakia of the vocal cord in a man with chronic hepatitis C infection treated with IFN and ribavirin. A 65-year-old man suffered from OLP before undergoing combination of IFN and ribavirin therapy for chronic hepatitis C. He was initially treated with IFNbeta (6 million units (MU) /day for 2 weeks), then a combination of IFNalpha-2b (6 MU/day for 2 weeks and 3 times a week for 14 weeks) and ribavirin (400-600 mg/day). The OLP lesion was not aggravated by application of steroids during the 7 weeks after the treatment, but after 18 weeks, the combination of IFN and ribavirin was stopped because of aggravation of the OLP. Elevated aminotransferase levels returned to normal during the therapy. But 7 weeks after discontinuation, aminotransferase levels rose to 10 times the normal range. Five months after discontinuation, the papules of CLP appeared. Eight months after discontinuation, the OLP erosion had gradually reduced, but some erosion remained. Aminotransferase levels were decreased, but serum HCV RNA had not disappeared. Caution should be exercised when IFN or ribavirin therapy is given to chronic hepatitis C patients with prior erosive OLP.