Summary. A systematic evaluation of published studies was undertaken to identify factors associated with accelerated fibrosis progression in patients with chronic hepatitis C virus (HCV) infection. An ecologic analysis was used to estimate relative risk (RR) of cirrhosis across four study methodologies: liver clinic series, post-transfusion cohorts, community-based studies and blood donor series. In each study category, the following factors were independently associated with disease progression: male sex (RR = 1.08); heavy alcohol consumption (RR = 1.61); elevated serum ALT levels (RR = 1.23) and histology demonstrating high-grade necro-inflammatory activity. After adjusting for these cofactors, older age at HCV infection and acquisition of HCV through blood transfusion were not implicated in influencing disease outcome. Although not able to be examined in this study,co-infection with HIV, and to a lesser extent HBV, is also likely to result in worse outcomes for patients with chronic HCV infection. Virological factors such as HCV genotype, viral load and quasispecies diversity are less likely to be important. A Weibull distribution was used to model disease progression at a population level. The influence of cofactors on individual prognosis was examined and an algorithm to predict the risk of subsequently developing cirrhosis is presented.