The mechanism responsible for the development of hepatocellular carcinoma (HCC) in the setting of oxidative stress has yet to be clearly defined. We studied the role of oxidative stress in hepatocarcinogenesis in subjects without underlying chronic viral hepatitis. The subjects were 24 patients negative for serum hepatitis B surface antigen and hepatitis C antibody tests, who underwent hepatic resection for HCC (Group N). Subjects were excluded if diagnosed with liver disease predisposing to HCC. Immunohistochemical staining for oxidative stress-related markers was performed on non-cancerous liver regions. Resected liver tissues adjacent to HCC from 24 patients with chronic hepatitis B (Group B) and 21 patients with chronic hepatitis C (Group C) were also examined. The percentage of 8-hydroxydeoxyguanosine-positive hepatocytes in Group N was significantly lower than that in Group B and that in the combined population of Groups B and C. The percentage of the area positive for 4-hydroxynonenal in Group N was significantly higher than that in Groups B or C. Meanwhile, the percentage of the area positive for manganese superoxide dismutase in Group N was not different from that in Groups B and C. In conclusion, the mechanism of hepatocarcinogenesis through oxidative stress for patients without known liver disease predisposing to HCC may differ from that for patients with chronic viral hepatitis.