The study was aimed at identifying the hepatitis C virus (HCV)-antibody status of prisoners incarcerated in South Australia in order to develop an HCV prevalence estimate for the whole prison system. The health records of persons incarcerated within eight prisons (accommodating approximately 93% of the jurisdiction's adult incarcerated population) were audited for evidence of HCV infection, age, sex, Indigenous status (Australian Aboriginal or Torres Strait Islander) and date of entry to prison. These data were analysed using both univariate and multivariate techniques. Among 1347 prisoners (1254 males and 93 females), 30.2% were HCV-antibody positive. After excluding those with no history of testing, HCV-antibody prevalence rose to 41.3% (males 39.8%, females 66.1%). HCV-antibody positivity was significantly associated with age, sex and Indigenous status in both univariate and multivariate analyses. Consistent with the literature, the prevalence of HCV infection in the SA prison system appears to be extremely high. This study suggests that HCV prevention efforts in prison settings should be considered as an important priority.