Platelet-derived endothelial cell growth factor (PD-ECGF) is expressed in the lining epithelial cells of ovarian endometriomas, and in interstitial cells of the subepithelial area with angiogenesis. The expression of PD-ECGF persists in endometriotic endometrium during the menstrual cycle. This might suggest that PD-ECGF contributes to the growth of ovarian endometriomas via subepithelial angiogenesis independently of the sex steroidal milieu.