In order to identify the risk factors for hepatitis C virus (HCV) infections, a case-control study was conducted from September 1993 to April 1994. HCV infection was confirmed by the second generation of recombinant immunoblot assay. Sixty-four cases and 128 controls matched for age and sex with a 1:2 ratio of cases to controls were enrolled. Exposure data were obtained from all participants by self-administered questionnaire and the odds ratios of possible risk factors of HCV infection analysed. Sixty-four cases consisted of forty-two patients with chronic hepatitis, nine with cirrhosis, one with hepatocellular carcinoma, and twelve with normal liver function. History of acute hepatitis (OR 3.9) and transfusion (OR 2.4) were associated with an increased risk of HCV infection. Operation, acupuncture, endoscopy, tooth extraction, tattooing, ear piercing, needle sharing and family history of hepatitis were not associated with an increased risk of HCV infection. In conclusion, transfusion remains the major route of transmission of HCV in Korea.