Assessment of prognosis from hepatitis requires liver histology. When the fibrosis stage is known, and if the fibrosis progression rate can be established, time to development of cirrhosis can be calculated. The fibrosis progression rate can be calculated from a single biopsy when duration of infection prior to biopsy is known. Sequential biopsies can also be examined. In this work, we studied histological activity and fibrosis stage in liver biopsies of 157 hepatitis C virus (HCV)-infected patients, including 92 for whom the approximate duration of infection was known. The mean fibrosis progression rate was 0.09 units per year, and was not influenced by mode of infection or viral genotype. Forty-six patients who had very mild histological changes in the initial biopsy underwent repeat biopsy 2 years later (with no intervening anti-viral treatment). Comparison of paired biopsies confirmed a tendency to histological progression and increasing hepatic fibrosis (mean, 0.15 fibrosis units per year). A normal baseline alanine aminotransferase (ALT) value was associated with slow fibrosis progression before baseline biopsy and between biopsies. These data do not differ from published cross-sectional and longitudinal studies, and suggest that histological progression will be observed during follow-up of most patients, including those with mild histological changes at time of initial assessment.