The TGF-β-stimulated Smad 2/3 signalling pathway was active in the peritoneum and there were significant increases (P<0.05) in expression of genes associated with tumorigenesis (MAPK8, CDC6), epithelial-mesenchymal transition (NOTCH1), angiogenesis (ID1, ID3) and neurogenesis (CREB1) in the peritoneum of women with endometriosis. Here, ID3 is linked to endometriosis.