A total of 172 Swedish patients treated with interferon-alpha for at least 24 weeks and followed-up > or =24 weeks after treatment was stopped were analysed for pre-treatment factors of importance for achieving a virological sustained response (SR). Furthermore, the predictive value for a virological SR of a positive or negative HCV RNA test at week 12 of treatment was evaluated. A low baseline viral load and genotype non-1b were pre-treatment factors indicating a favourable response. Thus, 44% (38/86) of patients with a low baseline viral load vs. only 16% (14/86) of those with a high viral load had a virological SR (p<0.0001). Of patients with a negative qualitative HCV RNA test after 12 weeks of interferon treatment, 46% (44/95) had virological SR, whereas only 5.9% (4/68) of those with a positive test had (p<0.0001). Prolonged ( > 6 months) treatment with interferon-alpha tended to increase the chance of virological SR (p<0.052).