[en] AIM: To evaluate the efficacy of early interferon alpha-2b in non-post-transfusion acute hepatitis C virus: a prospective study with historical comparison. PATIENTS: Group A: 28 patients prospectively treated for acute hepatitis C virus with daily regimen of interferon 5 million units for 2 months. Group B: historical series of 16 patients with untreated acute hepatitis C virus. RESULTS: There was no significant difference between the two groups with regard to gender, age, icterus, alanine aminotransferase, or genotypes. In group B, hepatitis spontaneously resolved in three of 16 (19%) patients (follow-up 1-7 years). In group A, 21 of 25 patients became sustained viral responders (75%; P = 0.0003 vs. group B). Factors include not predictive of sustained viral response: age, gender, sources of infection, presence of icterus, alanine aminotransferase peak, bilirubin peak, incubation period, presence of hepatitis C virus antibodies at presentation, or genotypes. The time from presentation to the start of therapy was, however, significantly shorter in sustained viral responders (43 +/- 31 days) than in relapsers or non-responders (88 +/- 52 days) (P = 0.016). CONCLUSIONS: Early treatment of acute hepatitis C virus with interferon prevents chronicity. A short waiting time from presentation to treatment appears as the most relevant predictive factor for sustained response.