Introduction: Ectopic ovarian tissue is an unusual entity, especially if it is an isolated finding thought to be of embryological origin.
Case presentation: An 11-year-old, morbidly obese female presented with left flank pain, nausea, and irregular menses. Various diagnostic procedures suggested a large ovarian cyst, and surgical resection was performed.
Conclusion: Histologically, the resected mass was not of tubal origin as suspected, but a serous cystadenoma arising from ovarian tissue. The patient's two normal, eutopic ovaries were completely uninvolved and unaffected. A tumor arising from ectopic ovarian tissue of embryological origin seems the most likely explanation. We suggest refining the descriptive nomenclature so as to more precisely characterize the various presentations of ovarian ectopia.