['We researched the molecular marker for prognosis of postoperative patients with hepatocellular carcinoma (HCC).', 'The association of amino acid substitutions in the hepatitis C virus (HCV) core region and hepatocarcinogenesis has recently been explored. We investigated if these amino acid substitutions are associated with recurrence or survival in patients with HCC after attempted curative treatment by hepatectomy.', 'A total of 163 patients infected with HCV genotype 1b who previously underwent hepatectomy for primary, not recurrent HCC were analyzed. Amino acid substitutions in the HCV core region were measured by direct sequencing. Postoperative recurrence or survival rates were compared according to tumor characteristics, tumor markers, and amino acid substitutions in the core region.', 'Recurrence rates after hepatectomy were higher in patients bearing a methionine at residue 91 of the HCV core region than in patients with leucine (P = 0.0002). Survival was also decreased in patients with methionine at this residue from that seen in patients with leucine at this position (P = 0.0061). The associations between amino acid substitutions at residue 91 of the HCV core region and either recurrence or survival rates were independent of liver function, progression of HCC, or tumor marker levels.'] Are amino acid substitutions in the hepatitis C virus core region associated with postoperative recurrence and survival of patients with HCV genotype 1b-associated hepatocellular carcinoma?