To assess the factors associated with the development of moderate and severe fibrosis, the medical records of 426 patients with chronic hepatitis C virus infection attended at the Infectious and Parasitic Diseases Clinic of the University of São Paulo Faculty of Medicine from January 1 to December 31, 2000 were reviewed. Of the patients included in the study, 56.3% were male and 43.7%, female. Patient age ranged from 18 to 69 years. Blood transfusion was the most frequent form of hepatitis C virus transmission, detected in 128 (30%) cases, and no risk factor was detected in 187 (43.9%) patients. Patient distribution regarding architectural changes observed in a liver biopsy was: grade 0 (14.1%); grade 1 (51.2%); grade 2 (20.6%); grade 3 (8%); grade 4 (6.1%). Multivariate analysis revealed a positive correlation between fibrosis severity and age greater than 40 years at the time of the liver biopsy, serum albumin levels below normal lower limits, gamma-glutamyltransferase levels equal to or higher than twice upper normal limits, platelet numbers less than 150,000/mm(3) and high necroinflammatory activity. The data obtained were inconclusive regarding a possible correlation between severity of fibrosis and alcoholism.