To clarify the characteristics of fibrosis developed in the process from chronic hepatitis C to cirrhosis, a morphometric analysis of liver biopsy samples was conducted on 25 chronic hepatitis C patients and 20 chronic hepatitis B patients (controls). Hepatitis C patients were followed up for 3 to 23 years. The mean number of liver biopsies performed on these patients was 3.8. Each biopsy was evaluated for the degree of fibrosis by using two methods: a semiquantitative method with a staging scoring system, and morphometry using a computed image analysis system. A significant correlation was observed between the Stage and the area of fibrosis (AF = the ratio of the area of fibrosis to that of the entire tissue specimen). The AF in cirrhosis was significantly higher in hepatitis C patients than in hepatitis B patients. The ratio of AF in the last biopsy sample to AF in the initial biopsy sample was significantly higher in hepatitis C patients than in hepatitis B patients. Evolution from chronic hepatitis C to cirrhosis occurred more frequently in patients aged > or = 50 years, and this time period was 1.8 times shorter than that in patients aged < 50 years. AF in the initial biopsy related significantly to the period of evolution from chronic hepatitis C to cirrhosis. AF in the initial biopsy might be a predictive factor for prognosis.