Background: Although ovarian tumors are most commonly observed in adults, they relatively rarely occur in children. The majority of ovarian masses encountered in the premenarchal or childhood stages are non-neoplastic lesions such as benign functional cysts. Epithelial tumors account for 8–10% of all ovarian tumors and are histologically classified as mucinous or serous. The most common benign epithelial ovarian tumor is cystadenoma.
Case Report: We report the case of a 14-year-old premenarchal girl with chronic abdominal pain, constipation, and abdominal enlargement. A computed tomography detected a huge left ovarian cystic tumor. A 9-kg ovarian tumor was removed surgically. Pathology showed a benign mucinous cystadenoma (MCA).
Conclusions: Ovarian neoplasms in children present a diagnostic quandary, and very often the diagnoses are missed or delayed. When the diagnosis is made, a prompt and fertility-preserving surgical treatment must be performed and followed to prevent recurrence.

Keywords: Cystadenoma, Mucinous - surgery, Adolescent, Laparotomy, Neoplasm Staging, Ovarian Neoplasms - surgery, Precancerous Conditions, Tomography, X-Ray Computed