Acute hepatitis C often progresses to chronic infection. We undertook a randomized controlled trial to determine whether short-term therapy with interferon (IFN) during acute hepatitis C is effective in preventing the development of chronic hepatitis. Thirty patients with acute hepatitis C were randomized into 1 of 2 treatment groups. IFN therapy was initiated 8 weeks after the onset of acute hepatitis in the early-intervention group and after 1 year of observation in the late-intervention group. Short-term therapy consisted of natural IFN-alfa (6 million units) administered on consecutive days for a period of 4 weeks. Any signs of recrudescence of disease were immediately followed by interval IFN therapy (3 times weekly for 20 weeks). In the early-intervention group, short-term therapy was associated with a sustained virological response in 13 of 15 patients (87%). Follow-up treatment was associated with a sustained virological response in both of the remaining 2 patients (100%). The sustained virological response rate was significantly higher in the early-intervention group (87%, 13 of 15 patients after short-term therapy alone, and 100%, 15 of 15 patients after short-term with or without follow-up therapy) than in the late-intervention group (40%, 6 of 15 patients after short-term therapy alone, and 53%, 8 of 15 patients after short-term therapy with or without follow-up therapy, P =.021 and P =.006, respectively). In conclusion, short-term (4 weeks) IFN treatment of patients with acute hepatitis C may be associated with satisfactory results, if initiated at an early stage of the disease.