Abstract Dendritic cells (DCs) are professional antigen-presenting cells that enhance and regulate both innate and acquired immune reactions. It has been reported that several viruses actively down regulate DC function to escape from host immune system. To clarify the involvement of DC in anti-hepatitis C virus (HCV) immune reactions, we compared DC function between chronic hepatitis C patients and healthy donors. Monocyte-derived DCs generated from patients were relatively immature and were impaired in allostimulatory capacity and IL-12 p70 production when compared to that from donors. In addition, MDC and PDC in HCV-infected patients were reduced in number and impaired in their ability to promote Th1 polarization. These results demonstrate that DCs are numerically and functionally impaired in HCV-infected patients, which is critically involved in the pathogenesis and persistence of HCV infection.