To address the relevance of EZH2 and other PRC2 components to endometriosis, we first performed an immunohistochemistry (IHC) analysis of EZH2, PRC2 constituent proteins (EED and SUZ12), H3K27me3 and H3K9me3 expression in eutopic (n = 14) and ectopic (n = 23) endometrial tissue samples from patients with ovarian endometrioma and in normal endometrial tissues (n = 24). This evidence concerns the gene EED and endometriosis.