AIM: Glutathione S-transferase mu 1 (GSTM1) and theta 1 (GSTT1) genes are involved in the metabolism of a wide range of carcinogens, but deletions of the genes are commonly found in the population. The present study was undertaken to evaluate the association between GSTM1 and GSTT1 gene polymorphisms and hepatocellular carcinoma (HCC) risk. METHODS: The genetic polymorphisms were studied at an aflatoxin highly contaminated region in Guangxi, China. Pdymerase chain reaction (PCR) technique was used to detect the presence or absence of the GSTM1 and GSTT1 genes in blood samples. The case group was composed of 181 patients of HCC identified by the pathologists and the control group was composed of 360 adults without any tumor. RESULTS: The frequencies of GSTM1 and GSTT1 null genotypes in the control were 47.8% and 42.7%, while those in the HCC group were 64.6% and 59.7%, respectively. The differences between HCC group and control group were very significant (P<0.01). GSTM1 and GSTT1 combined null genotypes in HCC group and control group were 38.2% and 18.5% respectively, and the difference was significant (P<0.05). CONCLUSION: The GSTM1 and GSTT1 null genotypes are associated with an increased risk of HCC in a special geographic environment. Combination of the two null genotypes in an individual is substantially increased twice the risk of HCC. AIM: Glutathione S-transferase mu 1 (GSTM1) and theta 1 (GSTT1) genes are involved in the metabolism of a wide range of carcinogens, but deletions of the genes are commonly found in the population. The present study was undertaken to evaluate the METHODS: The genetic polymorphisms were studied at an aflatoxin highly contaminated region in Guangxi, China. Pdymerase chain reaction (PCR) technique was used to detect the presence or absence of the GSTM1 and GSTT1 genes in blood samples. The case group was composed of 181 patients of HCC identified by the pathologists and the control group was composed of 360 adults without any tumor. RESULTS: The frequencies of GSTM1 and GSTT1 null genotypes in the control were 47.8 % and 42.7%, while those in the HCC group were 64.6% and 59.7% respectively. The differences between HCC group and control group were very significant (P <0.01). GSTM1 and GSTT1 combi ned null genotypes in HCC group and control group were 38.2% and 18.5% respectively, and the difference was significant (P <0.05). CONCLUSION: The GSTM1 and GSTT1 null genotypes are associated with an increased risk of HCC in a special geographic environment. Combination of the two null genotypes in an individual is substantially increased the risk of HCC.