Hepatitis C virus (HCV) is a common chronic bloodborne virus infection that affects an estimated 2.7 million persons in the United States. HCV infection causes an estimated 8,000-10,000 deaths each year from cirrhosis and hepatocellular carcinoma and is the leading reason for liver transplantation. Because injection drug use is a major risk factor for both human immunodeficiency virus (HIV) and HCV transmission, publicly funded HIV counseling and testing sites (HIV CTS) may have a role in HCV prevention. To evaluate the need for HCV services at these sites, the Connecticut Department of Public Health (CDPH) conducted an anonymous HCV seroprevalence study among clients of HIV CTS. This report summarizes the results of this analysis, which indicate that, among clients of these HIV CTS, the prevalence of antibody to HCV (anti-HCV) was 9.8%, compared with 1.3% for HIV, with significantly higher prevalence among clients of substance abuse treatment sites (40.2%), compared with other sites (6.9%). HCV counseling and testing should be integrated into all HIV CTS, especially those associated with substance abuse treatment.