Ten years after the discovery of the hepatitis C virus (HCV) and its association with NANB hepatitis as a major cause of chronic liver disease worldwide, our knowledge of the natural history of hepatitis C is still limited. The asymptomatic course of the disease in most patients, its slow and silent progression and heterogeneous outcome and the widespread use of interferon therapy during the past decade explain why many questions are still unsolved. The changing epidemiological pattern of HCV and the significant contribution of several cofactors to the severity of liver disease also complicate the development of a general model describing the natural history of hepatitis C. Available data indicate that HCV infection may resolve without any clinical signs of liver disease in individuals exposed to low dose inoculum and that these cases may develop T cell immunity even in the absence of anti-HCV seroconversion. Rates of complete biochemical and virological resolution of acute hepatitis C range between 10 and 50%, and are probably affected by the route of infection, size and type of inoculum and acute phase clinical features. Chronic HCV infection may develop with or without ALT abnormalities and with or without chronic inflammation and increasing fibrosis in the liver. Studies conducted in patients who acquired hepatitis C by blood transfusion 15-25 years ago indicate that 20-30% of them have now progressed to cirrhosis, including 5-10% with end stage liver disease and 4-8% who died of liver-related causes. Similar studies conducted in patients infected by other routes have shown a more benign course of hepatitis C, with little evidence of cirrhosis and no liver-related mortality during the first two decades. Outcomes after longer follow-up need to be assessed. In patients presenting with chronic hepatitis C, fibrosis progression is extremely variable over time and can be partially predicted by the age at infection, disease duration, liver histologic activity and stage of fibrosis and by the ALT profile. However, it is often difficult to predict clinical outcomes in individual cases. In patients who have developed cirrhosis, the 5-year risk of decompensation is between 15 and 20% and that of hepatocellular carcinoma around 10%. Several variables have been shown to influence the natural course of shown C, the most significant being age at infection, alcohol consumption and coinfection with HBV and HIV Studies are being performed to assess the role of host genetics. Viral factors, such as the HCV type and load, seem to have inconsistent or marginal effects.