Because hepatocellular carcinoma often recurs after surgical resection or ethanol injection therapy, we conducted a prospective randomized controlled trial of interferon (IFN) in patients with chronic liver disease caused by hepatitis C virus (HCV). Twenty eligible patients with cirrhosis were randomized into two groups: 10 patients treated with 6 million units of natural IFN-beta twice a week for 36 months and 10 patients without IFN therapy. One patient within the treatment group discontinued interferon therapy after 19 months of treatment because of a mild degree of retinopathy. None of the patients in either group lost HCV-RNA until the end of the observation. Although 7 (70.0%) of 10 patients in the nontreatment group showed tumor recurrence, only 1 (10.0%) of 10 patients with IFN therapy developed tumor recurrence during a median observation period of 25.0 months. Cumulative recurrence rates of the treated and untreated groups were 0% and 62.5% at the end of the first year, and 0% and 100% at the second year, respectively (log-rank test, P =.0004). In conclusion, intermittent administration of IFN suppressed tumor recurrence after treatment with surgery or ethanol injection in patients with HCV-related chronic liver disease.