Antibody-negative hepatitis C virus (HCV) infection, defined by the presence of HCV viremia in the absence of a serologic response to HCV, was detected in two immunocompetent and symptom-free children; each had a history of exposure to blood products. HCV infection may occasionally explain cryptogenic elevation of aminotransferases, even in the absence of serum anti-HCV. HCV-RNA should be investigated in these cases, particularly in the presence of previous exposure to blood products.