Oral cancer accounts third of all malignancies in India. Tobacco use, the major etiological factor for oral cancer is known to generate free radicals resulting in alterations in antioxidant enzymes like, glutathione-S-transferase (GST), glutathione reductase, superoxide dismutase, catalase, and glutathione peroxidase as well as lipid peroxidation and total thiol. Therefore, it is of fundamental importance to evaluate the role of tobacco and antioxidant enzymes and oxidative stress markers in oral carcinogenesis.One hundred forty oral cancer patients and 50 healthy controls, classified as "habitual controls" and "nonhabitual controls" having tobacco habits and no tobacco habits, respectively, were included in the study. Adjacent normal and malignant tissue samples were also collected. Erythrocyte, plasma, and tissue levels of antioxidant enzymes and total thiol were assayed by spectrophotometric methods. GSTM1 genotype was analyzed using polymerase chain reaction.Antioxidant enzymes were significantly higher whereas glutathione peroxidase and thiol levels were lower in patients as compared with habitual controls. Habitual controls with higher tobacco exposure and lower antioxidant enzymes as well as thiol showed higher risk of oral cancer development. Antioxidant enzymes were higher, whereas catalase and thiol levels were lower in malignant as compared with adjacent normal tissues. Sixty-three percent of the patients showed GSTM1 null genotype.The study showed risk of oral cancer development in habitual controls with lower antioxidant enzymes, lower oxidative stress markers, and higher lifetime tobacco exposure. Individuals with GSTM1 null genotype may be at higher risk of oral cancer development.