Malignant ovarian tumors are exceedingly rare in children. The overwhelming majority of ovarian masses in the pediatric population are benign. Distinguishing benign from malignant ovarian pathology can be challenging. Avoidance of oophorectomy for benign ovarian disease and potential fertility sparing surgery for ovarian malignancy are crucial preoperative risk stratification steps for the healthcare team. The presentation of malignant ovarian tumors in girls is often non-specific, and may include abdominal pain and distention, palpable abdominal or pelvic mass, hirsutism or virilization. When evaluating young girls presenting with ovarian masses, it is important to consider their clinical characteristics, as ovarian masses in young, pre-pubescent girls are more likely to be malignant. Imaging should include abdominal-pelvic US, and axial imaging (CT or MRI). Serum tumor markers are essential elements of the work up includingCA-125, β-hCG, AFP, estradiol, testosterone, inhibin, LDH, and FSH. Germline mutations and cancer predisposition syndromes are associated with malignant ovarian tumors. Malignant ovarian masses are categorized into epithelial and non-epithelial subtypes. Epithelial tumors are the most common type of ovarian tumor in adult women. Non-epithelial tumors are most frequent in children. Non-epithelial tumors include the germ cell tumors (most frequent malignant tumor in children), and sex-cord stromal cord tumors. The Fédération Internationale de Gynécologie et d'Obstétrique (FIGO) staging classification is used for staging epithelial tumors and sex-cord stromal tumors and the Children’s Oncology Group (COG) staging is used for staging of germ cell tumors. The goal of treatment for all malignant ovarian tumors is complete resection and adjuvant platinum-based chemotherapy may be necessary for advanced stages. In the pediatric population, fertility sparing surgery should always be included in preoperative decision-making and family counseling.