Deep infiltrating endometriosis is characterized by the presence of nodular lesions largely composed of fibromuscular tissue. Transforming growth factor beta 1 (TGF-beta1) is the cytokine most causatively associated with disorders characterized by fibrosis throughout the body. Therefore, the hypothesis was tested that mechanisms increasing the fraction of biologically active TGF-beta1, such as TGF-beta 1 gene polymorphisms, lead to an increased risk of developing deep infiltrating endometriosis. The frequency of the -509C/T polymorphism of the TGF-beta 1 gene was tested in women with deep infiltrating endometriosis (n = 72), gynecological patients without symptoms of endometriosis (n = 95) and healthy females (n = 93). Detection of the -509C/T polymorphisms was performed using PCR-restriction fragment length polymorphism analysis. We did not observe statistically significant differences in the frequency of the -509C/T polymorphism between the groups. Our study does not support an association between the -509C/T polymorphism of the TGF-beta 1 gene and an increased risk of deep infiltrating endometriosis.