Currently, the second- and third-generation enzyme immunoassays (EIA-2 and EIA-3) for hepatitis C virus antibody (anti-HCV) are the most practical screening tests for the diagnosis of HCV infection. The need for and the choice of supplementary or confirmatory tests depend on the clinical setting and the likelihood of a true-positive EIA result. Detection of HCV RNA in serum by polymerase chain reaction (PCR) assay is the gold standard for the diagnosis of HCV infection. However, the lack of uniformity in current PCR assays has tarnished this standard. Confirmatory tests for the diagnosis of HCV infection are in general unnecessary in anti-HCV-positive patients who present with chronic liver disease. When indicated, the most appropriate test in this setting is a qualitative PCR assay for HCV RNA. Confirmatory tests should always be performed in anti-HCV-positive blood donors and individuals with normal aminotransferase levels. The most appropriate approach is to retest for anti-HCV using recombinant immunoblot assay (RIBA) and then test for HCV RNA using PCR assay in those who are RIBA positive or indeterminate. Liver histology is the gold standard in assessing severity of liver disease. Quantitative tests for serum HCV RNA levels do not help to determine the severity of liver disease. At the moment, HCV genotyping should be considered a research tool and not a part of the diagnostic work-up in clinical practice. The goals of treatment for chronic hepatitis C are sustained biochemical and virological response. Viral clearance should be determined by qualitative PCR assay. Quantifying serum HCV RNA level can help in predicting response to interferon treatment, but further studies using more standardized assays are needed to determine if these values can be used to select patients for treatment.