Objectives: Malignant and borderline ovarian tumors of epithelial origin are rarely encountered among prepubertal girls and adolescents. The aim of this population-based study was to elucidate their clinicopathological characteristics and prognosis using a multi-institutional tumor registry. Study design and outcomes: The National Cancer Institute's Surveillance, Epidemiology, and End Results database was accessed and a cohort of females aged <= 19 years old, diagnosed between 1988 and 2013 with a borderline ovarian tumor (BOT) or a malignant epithelial ovarian carcinoma (EOC) was accessed. Observed survival (OS) was assessed using the Kaplan-Meier method. Comparisons were made using the log-rank test. Results: A total of 114 cases diagnosed with BOT between 1988 and 2000 were identified; 61/114 (53.5%) and 51/114 (44.8%) of BOT were of serous or mucinous histology respectively. Ten-year OS for those with BOT was 97.3%. A total of 140 cases of EOC were identified. Median age was 17 years and the most common histological subtypes were mucinous 79/140 (56.4%) and serous 29/140 (20.7%) adenocarcinoma. Most had stage I disease 92/131 (70.2%) and fertility-sparing surgery was commonly performed. Five-year OS for those with stage I disease was 93.6% compared to 48.3% for cases with exta-ovarian tumor spread (p < 0.001). Conclusions: BOT and EOC are exceedingly rare in the pediatric and adolescent population. In this age group EOC consists mostly of low-grade mucinous and serous tumors confined to the ovary. OS survival for those with stage I disease is excellent. (C) 2016 Elsevier Ireland Ltd. All rights reserved.