OBJECTIVE Hepatitis B or C virus infection is considered to be the main cause of hepatocellular carcinoma (HCC) in Japan. Aflatoxin B1 (AFB1) is a carcinogen associated with HCC in regions with high exposure. Mutations in codon 249, exon 7 are a hallmark of AFB1 exposure. Therefore, to clarify the role of AFB1 in hepatocarcinogenesis, we examined AFB1-DNA in liver tissue and sequenced TP53 in Japanese patients with HCC. METHODS Hepatocyte AFB1-DNA adducts were determined immunohistochemically and direct sequencing of TP53 was done to determine mutations in 188 of 279 patients who underwent hepatic resection for HCC. We assessed hepatitis C virus antibodies (HCV Ab) and HBSAg expression; patients without either were defined as having non-B non-C hepatocellular carcinoma (NBNC HCC). RESULTS AFB1-DNA adducts were detected in hepatocyte nuclei in 18/279 patients (6%), including 13/83 patients (16%) with NBNC HCC and 5/51 patients (10%) expressing hepatitis B surface antigen. None of the patients with HCV Ab (n=136) were positive for AFB1-DNA. The incidence of the G-T transversion and mutations in exon 7 of TP53 in patients with AFB1-DNA adducts were significantly higher in patients with than in patients without AFB1-DNA adducts. All three patients with the codon 249 AGG-AGT mutation had AFB1-DNA adducts. CONCLUSIONS Although exposure to AFB1 is thought to be low in Japan, it is still associated with hepatocarcinogenesis, particularly in NBNC HCC and hepatitis B individuals.