The aim of this study is to identify the risk factors associated with anti-HCV positive status in a Bunun aboriginal community in Taiwan. In a door-to-door survey we collected 712 blood samples, and employed an enzyme immunoassay for anti-HCV to detect the recombinant antigen of viral genome including one structural and two nonstructural proteins. The prevalence of anti-HCV was 16.9% for the whole community covering an age range of five years to 84 years, but it was 48% in individuals older than 45 years. The calculated annual incidence rate was 1.25%. Information about possible risk factors was obtained from questionnaires completed in 1992. Age, sex, village of residence, educational level, and the extraneous factor of having been iatrogenic injected during a period one or two years before the survey, showed a significant association with positive anti-HCV status. A dose response relationship between the rate of positive anti-HCV status and frequency of injections was found statistically significant (P < 0.001). Accordingly, a second visit was made to find the possible infection source, and according to information obtained from the recall of 211 interviewees, an illegal medical service was suspected of spreading the recent infection.