To improve understanding of glutathione S-transferase (GST) behavior in terms of a development and prognostic factor for gastric adenocarcinoma, we investigated the association between the GSTM1 and GSTT1 null genotypes and gastric cancer risk or the prognostic value of the GSTM1 and GSTT1 null genotypes was evaluated. Using a polymerase chain reaction-based method, the frequencies of GSTM1 and GSTT1 genotypes and prognostic factors, such as staging, differentiation, and histologic type (intestinal vs. diffuse), were evaluated in 80 patients with curatively resected primary gastric adenocarcinoma. The frequencies of GSTM1 and GSTT1 null individuals were higher in the gastric cancer group, but the differences were not statistically significant (for GSTM1 null odds ratio (OR)=0.86; 95% confidence interval (CI)=0.49-1.51 and for GSTT1, OR=0.97; 95% CI=0.55-1.71). Since the GSTM1 and GSTT1 null genotypes are potential indicators of gastric adenocarcinoma, we examined the relationship between the GSTM1 and GSTT1 genotypes and prognostic factors. In terms of the histologically diffuse type of cancer, GSTM1 indicated an approximately 3.24-fold increase (OR=3.24; 95% CI=1.05-10.17). With respect to gastric cancer differentiation, the frequency of the GSTM1 null genotype was linked with a statistically significant increase in risk (3.42-fold) for the high-grade type (OR=3.42; CI=1.02-13.24). Our results indicate that there is no obvious relationship between GSTM1 and GSTT1 polymorphisms and the development of gastric cancer. However, in Korean gastric adenocarcinoma patients the GSTM1 null genotype appears to be associated with a poorer prognosis.