OBJECTIVES: Hepatitis C virus is a Bloodborne virus causing hepatitis C, which is correlated to liver cirrhosis and liver cancer. Recently, new drug class called direct acting agent (DAA) with near 100% efficacy was developed. With these new medications to be available soon, it is necessary to estimate the cost of illness of HCV patients precisely to conduct the pharmacoeconomic evaluation. This study aims to estimate direct medical costs of HCV patients in South Korea using national health insurance claims data. METHODS: A dataset called Health Insurance Review & Assessment service National Inpatient Sample (HIRA-NIS) was used to estimate direct medical costs. Data of patients with HCV disease code were obtained. All of the patients had comorbid diseases and those with liver cancer or cirrhosis were included for medical cost analysis, assuming they were caused by chronic HCV.  RESULTS: Among 1.1 million inpatients and outpatients, 7008 patients were diagnosed with HCV. Among them, 306 patients had liver cancer, 717 patients had cirrhosis and 382 had both liver cancer and cirrhosis as comorbid diseases. Annual medical costs per patient for each health state were $7,830, $3,000 and $10,160 for liver cancer, cirrhosis, and both respectively. The obtaining medical cost of HCV state was impossible since there was no patient with HCV only in the database. CONCLUSIONS: Compared to the prevalence from the previous epidemiologic study, the weighted percentage of the patients diagnosed with HCV in this study was significantly low(0.78% vs. 0.21%). It is lower because most patients get screened for HCV when symptoms appear due to comorbidity while HCV infection itself is usually asymptomatic. Thus, using health insurance claims data, medical costs of HCV-related liver cancer or cirrhosis can be obtained, but not of HCV by itself.