The glutathione S-transferase (GST) family of enzymes is involved in the protection of the cell against foreign compounds and may consequently play a role in the development of cancer. Two of the family members, GSTA1 and GSTO1, have only been considered in a very limited number of studies. The objective of this study was to evaluate the potential relationships between GSTA1 and GSTO1 polymorphisms and breast cancer, taking into account the estrogen receptor statuses of the tumors and potential interactions with smoking, and intake of fruits and vegetables. The basis for the study was a nested case–control study including 396 postmenopausal pairs. Genetic polymorphisms were determined by restriction-fragment length polymorphism–polymerase chain reaction methods, and risks for breast cancer were estimated using conditional logistic regression. No association between GSTA1 polymorphism and breast cancer was found whereas carriers of the GSTO1 *B/*B genotype had higher risks of breast cancer when compared with carriers of the GSTO1 *A/*A genotype (incidence rate ratio 1.62, 95% confidence interval: 1.01–2.61). This association was strongest with regard to estrogen receptor positive breast cancer (incidence rate ratio 2.16, 95% confidence interval: 1.21–3.84). No signs of interaction with smoking or intake of fruits and vegetables were found for either GSTA1 or GSTO1 polymorphism. The study suggests that postmenopausal carriers of the GSTO1 *B/*B genotype may be at increased risk of especially estrogen receptor positive breast cancer. The finding of a higher risk with this genotype is in accordance with the only previous study. Further research is needed to confirm the finding.