Background/Aims: A high prevalence of HBsAg in leprous patients has been reported. Hepatitis C virus(HCV) and Hepatitis B virus(HBV) are transmitted by a similar route. There are few studies about the prevalence of HCV infection in the leprous patients, therefore this study was conducted. Methods: This study included 96 leprous patients and 47 controls, who were non-leprous family members of the leprous patients. Antibody HCV by MEIA and recombinant immunoblot assays(RIBA) was checked. HBV markers(HBsAg, anti-HBs, and IgG anti-HBc by MEIA) were checked to evluate the evidence of past or present HBV infection. Results: Antibody HCV was detected in 67.7%(65/96) of the leprous patients. RIBA tests in HCV antibody positive leprous patients showed reactive responses in 81.5%(53/65), intetmediate responses in 10.8%(7/65) and nonreactive response in 7.8%(5/65) respectively. The seroprevalence of antibody to HCV in leprous patients was higher than that of controls(10.6 %, 5/47) and that of the general population in Korea(0.54-1.7%), and it increased with age and duration of the ]eprosy contraction. The risk factors of HCV infection such as transfusion, operation, tattoo, acupuncture, and ear piercing were not associated with HCV seropositivity in the most leprcius patients. The seroprevalence of antibody to HCV was similar in multibacillary(69.7%) a.nd paucibacillary (65.5%) types. The rate of HBV marker positivity in leprous patients was higher(88.5%; 85/96) than that(55.3%; 26/47) than the control group, but HBsAg positivity was similar in both groups( 8.3% vs 12.8%). Conclusions: These results show that leprous patients are at a high risk of HCV infection and that the transmission route was not apparent in most cases. Therefore patients infected with HCV should be monitored regularly for liver function ad other hepatic complications, and, methods to control HCV infection among noninfected leprous patients shou]d be considered. (Korean J Gastroenterol 1997; 30:486-494)