The frequencies of the TG and TT genotypes were found to be significantly higher in the endometriosis group than in the control group. The frequency of the mutant T allele was higher in endometriosis compared with the control group./Our study showed a 10-fold increased risk of developing endometriosis with the presence of the mutant T allele. These findings support the notion that genetic variations in the endothelial NOS gene might contribute to endometrial angiogenesis and abnormalities in the development and function of human reproductive organs, affecting endometrial cell physiology. Here, NOS3 is linked to endometriosis.