Recent years have seen a growing evidence of ethnic differences in the frequency of glutathione S-transferase omega 1 (GSTO1) A140D gene polymorphism, which is associated with various cancers such as breast and liver. Until now however, no association has been investigated between the GSTO1 A140D polymorphism and lung cancer. The aim of our study was to see if there was one in the Turkish population. To do that, we identifi ed GSTO1 A140D polymorphism in 214 unrelated healthy individuals and 172 patients with non-small cell lung cancer (NSCLC) using the polymerase chain reaction -restriction fragment length polymorphism (PCR-RFLP) method. The frequencies of A/A (wild type), A/D (heterozygous mutant), and D/D (homozygous mutant) GSTO1 A140D genotypes in healthy subjects were 48 %, 41 %, and 11 %, respectively. In NSCLC patients they were 48 %, 45 %, and 7 %, respectively. We found no signifi cant association between the GSTO1 A140D gene polymorphism and NSCLC or its histological subtypes, namely squamous cell carcinoma or adenocarcinoma. Furthermore, this polymorphism did not correlate with smoking. Our study is the fi rst to show that the frequency of GSTO1 A140D gene polymorphism in the Turkish population is similar to other Caucasian populations and that this polymorphism is not associated with susceptibility to NSCLC.