HCV infection triggers a strong humoral and cellular response, which can be directed against specific virus antigens expressed on the surface of infected hepatocytes cellular membrane. Amongst the variety of produced antibodies a special role is attributed to antibodies against the core antigen, which are the first ones produced in early response to HCV infection. The aims of this research were evaluation of the occurrence of IgM antibodies against HCV core antigen in children with hepatitis C and analysis of the correlation between these antibodies presence and HCV RNA presence in children with chronic hepatitis C. The study comprised 30 children (10 girls, 20 boys) aged from 3 years and 7 months to 18 years. In all of them chronic hepatitis C was diagnosed basing on the current criteria. The control group comprised 10 children with anti-HCV antibodies in whom HCV RNA was not detected. In all the children the presence of antibodies against HCV, HCV RNA and antibodies against core antigen was tested. The conducted examinations revealed the presence of IgM antibodies against HCV core antigen in 13 out of 30 children (43.3%) with HCV RNA. These antibodies were not detected in any of the children from the control group. The research demonstrated a correlation between the presence of IgM anti-core antibodies and the presence of HCV RNA in children with chronic HCV infection. The correlation between the presence of HCV RNA and IgM anti-core suggests that these antibodies may be used as a serological marker of replicative activity of virus in children with chronic hepatitis C.