Glutathione transferases (GSTs), a multiple gene family of phase II enzymes, catalyze detoxifying endogenous reactions with glutathione and protect cellular macromolecules from damage caused by cytotoxic and carcinogenic agents. Glutathione S-transferase p1 (GSTP1), the most abundant GST isoform in the lung, metabolizes numerous carcinogenic compounds including benzo[a]pyrene, a tobacco carcinogen. Previous studies suggest that genetic polymorphisms of GSTP1 exon 5 (Ile105Val) and exon 6 (Ala114Val) have functional effects on the GST gene product resulting in reduced enzyme activity. Individuals with reduced GST enzymatic activity may be at a greater risk for cancer due to decreased detoxification of carcinogenic and mutagenic compounds. Utilizing a hospital-based case-control study, we investigated the association between GSTP1 polymorphisms at exons 5 and 6 with lung cancer risk. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was used to successfully genotype the GSTP1 exons 5 and 6 polymorphism in 582 Caucasian lung cancer cases and 600 frequency matched Caucasian controls. There was no association between the exon 5 variant genotypes (A/G+G/G) and overall lung cancer risk (OR=1.09; 95% CI 0.82-1.45) nor when stratified by age, gender, and smoking status. However, the exon 6 variant genotypes (C/T+T/T) were associated with a statistically significant elevated lung cancer risk (OR=1.40; 95% CI 1.06-1.92). Additionally, there was an increase in lung cancer risk for the exon 6 variant genotypes in younger individuals (<62 years) (OR=1.63; 95% C.I. 1.07-2.49) but no effect in older individuals (OR=1.14; 95% CI 0.72-1.81). A statistically significant increased risk of lung cancer was also observed for the exon 6 variant genotypes among men (OR=2.17; 95% CI 1.41-3.33), but not among women (OR=0.80; 95% CI 0.51-1.28). Among ever smokers, the exon 6 variant genotypes were associated with an elevated lung cancer risk (OR=1.58; 95% CI 1.14-2.19), which was not evident for never smokers (OR=0.53; 95% CI 0.21-1.33). These data demonstrate that the GSTP1 exon 6 polymorphism, but not the exon 5 polymorphism, is associated with lung cancer risk that is especially evident in men, younger individuals, and ever smokers.