In this study, we have demonstrated that TGF-β1 is increased in the peritoneal fluid of women with endometriosis, and that TGF-β1 and TGF-β signalling targets associated with cell cycle control, angiogenesis, EMT and tumorigenesis are significantly increased in the peritoneum of women with endometriosis compared to those without. The gene discussed is TGFB1; the disease is endometriosis.