Ovarian surface epithelial cells (OSEs) are considered to be the common source of endometrioma and epithelial ovarian cancer. The present study reveals that keratinocyte growth factor receptor (KGFR) messenger RNA was expressed in OSEs of endometriomas but not in those of normal ovaries, suggesting that autocrine KGF/KGFR and paracrine fibroblast growth factor 10/KGFR signaling loops may be involved with the proliferation in OSEs of endometrioma.