Patients with chronic infection with the 3a genotype of hepatitis C virus (HCV) are considered as 'easy-to-treat' with interferon/ribavirin (IFN/RBV), independent of liver disease severity. However, patients with extensive fibrosis or cirrhosis were under-represented in all the registration Phase III trials performed so far. To assess the influence of liver fibrosis on the outcome of anti-HCV therapy, all patients with genotype 3a hepatitis C who were naive to IFN-based therapies, and received RBV combined with standard IFN or pegylated IFN-(alpha2b (peg-IFN-alpha2b) as standard of care for their disease, were investigated at our centre. A sustained virological response (SVR) was achieved in 68 of 91 patients (75%) independent of IFN type, pretreatment viraemia, clearance of HCV RNA at week 4 and relevant co-morbidities. A SVR was less common in cirrhotics (6 of 17) than in non-cirrhotics (62 of 74; 35% vs 84%; P<0.0005). Compared to non-cirrhotics, the age and sex adjusted odds ratio (OR) of treatment failure for cirrhotics was 10.1 (95% confidence interval: 2.4-41.7). By multivariate analysis, cirrhosis was the only predictor of non-SVR. In conclusion, cirrhosis is an independent predictor of IFN/RBV treatment failure in patients chronically infected with HCV 3a and is associated with an increased risk of post-treatment hepatitis relapse. Evaluation of liver fibrosis is important in the management of patients with genotype 3a hepatitis C, since it helps to predict response to IFN/RBV therapy.