Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 57 2 2019 03 12 134 137 EN Leila Pourali Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Farokh Seilanian Toosi Department of Radiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Atiyeh Vatanchi Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Ali Taghizadeh Surgical Oncology Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. Zahra Rastin Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. 2018 07 25 2018 11 10 Ovarian tumors are rare in childhood and adolescent age. A 14-year-old girl presented with abdominal distention and mild cyclical abdominal pain since 3 months ago. There was an abdominal distention, and huge firm mass was palpated from pelvis to epigastric region. Abdominal ultrasonography revealed normal uterus and large multiloculated adnexal mass with multiple fine septations. Laparotomy was performed, and the ovarian mucinous borderline tumor was reported in frozen section biopsy. Exploration of other abdominopelvic organs revealed no other pathological signs. The final pathological report showed the right ovarian mucinous borderline tumor. Although the mucinous ovarian borderline tumor is a rare condition in adolescent age, pelvic mass, especially with solid or nodular component, must arise this diagnosis, and exploratory laparotomy with comprehensive surgical staging with regard to fertility preservation is warranted. https://acta.tums.ac.ir/index.php/acta/article/view/7403 https://acta.tums.ac.ir/index.php/acta/article/download/7403/5224