It is well established that hypoxic microenvironment contributes to breast cancer progression by activation of transcriptional genes that promote angiogenesis. By promoting the antioxidant activity of glutathione, glutathione S-transferases (GSTs) are likely to facilitate the hypoxia-inducible factor-1α (HIF-1α) activity, therefore stimulating the angiogenesis. We investigated herein the influence of the GSTM1 and GSTT1 polymorphisms in the intratumoral angiogenesis of 87 patients with sporadic breast cancer. The intratumoral microvessel density (IMVD) of formalin-fixed paraffin-embedded tissues samples from all patients was determined by immunohistochemistry. The high IMVD was defined as a median microvessel counting higher than 18.7 after the analysis of histogram with all the results. The high IMVD was more common in patients with the GSTT1 wild genotype than in those with the GSTT1 null genotype (P = 0.04). Our results suggest, for the first time, that the GSTT1 polymorphism constitutes an inherited determinant of intratumoral angiogenesis in sporadic breast cancer.