Results indicated that the self-reported and biologically observed prevalence of HIV were identical (22 percent) but the self-reported and biologically observed prevalence of HCV differed. The self-reported prevalence of HCV was 52 percent compared to the biologically observed HCV prevalence rate of 73 percent. This suggests that 30 percent of HCV-infected drug users were unaware of their HCV status. Moreover, among drug users under 30 years of age, 44 percent were HCV positive, suggesting that they were infected early during their drug use. The findings suggest that the French harm reduction campaign had a significant impact on HIV transmission among drug users but a limited impact on HCV transmission. The authors recommend that access to screening and treatment for HCV should be more widely available and they call for drug abuse to be viewed from a public health perspective rather than from a moral standpoint. Participants were 117 male and 49 female drug users recruited from all levels of the care network specializing in treatment for drug users. Participants completed an interviewer-administered questionnaire that focused on their sociodemographic information, their own evaluation of their health status, access to treatment and prevention services, withdrawal attempts, knowledge of risk factors, risk-taking behaviors, and sexuality. Participants also provided capillary blood collected on filter paper for serological analysis. The data from the questionnaires was then compared to the biologically observed data on HIV and HCV infection. Future research should focus on the relationship between drug users’ reluctance to be screened for HCV and their perceptions of treatments for the disease. Figure, tables, references