Two hundred and twenty-six patients who received blood products for open-heart surgery in childhood were screened by a second-generation enzyme-linked immunosorbent assay and with surrogate markers for hepatitis C virus (HCV) infection, such as alanine aminotransferase (ALT). Twenty-two (14%) of the 161 recipients who received blood products before 1989 and none of the subjects who had received blood products after 1990 (the year that the blood bank began to screen for HCV antibody) were HCV seropositive. Virologic and histologic studies showed that 10 (45%) of 24 seropositive patients had persistent hepatitis C virus infection, many with ongoing hepatitis. The remaining 12 seropositive patients with absent HCV RNA had normal ALT levels, indicating resolved hepatitis C infection. Enrolment in screening is important to detect chronic hepatitis C in children who received blood products prior to screening of blood donors for HCV antibody.