The recent advent of non-invasive methods for assessment of fibrosis allows serial assessments in all patients with hepatitis C. The aim of this prospective study was to evaluate changes in liver fibrosis, as measured with non-invasive methods, in a large cohort of HCV-infected patients with and without treatment. From May 2003 through March 2006, all previously untreated HCV-infected patients were enrolled in this study. Liver fibrosis was staged with FibroScan and Fibrotest at inclusion, then every year in untreated patients, and at the end of treatment and 6 months later in treated patients. The study population consisted of 416 patients, of whom 112 started treatment after enrolment. In the treatment group, FibroScan and Fibrotest values were significantly higher before and after treatment than in untreated patients at baseline and after 1 year. However, there was no significant difference between treated and untreated patients at the end of follow-up. FibroScan and Fibrotest values fell in all treated patients, whatever their virological response. In multivariate analysis, treatment was the only factor independently associated with a fall in the FibroScan value. In conclusion, whatever the virological response, treatment for HCV infection is associated with an improvement of FibroScan and Fibrotest values. Further studies are needed to compare these non-invasive methods with liver biopsy. These non-invasive methods, and especially FibroScan, should be useful for assessing treatment efficacy in clinical trials of new drugs.