Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 2 4 2018 05 14 91 93 EN Fakhrolmolouk Yassaee Department of Obstetrics and Gynecology, School of Medicine AND Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Hajar Abbasi Department of Obstetrics and Gynecology, School of Medicine AND Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 2017 09 24 2017 12 27 Endometrioma (ovarian endometrial cyst) usually occurs in women of reproductive age. We report a rare case of huge ovarian endometrioma that was as large as a watermelon. A 26-year-old woman from Iran complained of abdominal distention over approximately 9 months. Diagnostic imaging revealed a semi solid mass measured about 25 centimeter. After doing laparotomy, an ovarian endometrioma was diagnosed in pathology. https://crcp.tums.ac.ir/index.php/crcp/article/view/134 https://crcp.tums.ac.ir/index.php/crcp/article/download/134/88