A variety of non-neoplastic, tumor-like lesions occur in the ovary, some of which are listed in the World Health Organisation Classification of Female Genital Tumours, 5th edition (WHO 2020). The WHO-listed lesions are described briefly below, followed by a brief consideration of endometriosis.

Ovarian tumor and non-neoplastic lesions present a great challenge to Gynecological Oncologist. Certain non-neoplastic lesions of the ovary frequently form a pelvic mass and potentially mimic an ovarian neoplasm. Their proper recognition and classification is therefore important to allow appropriate therapy [6].

Non neoplastic lesions are mostly incidental findings. However the detailed knowledge of these lesions is helpful in the differential diagnosis of ovarian neoplasms.

Six nonneoplastic ovarian lesions (or alterations) are associated with pregnancy or the puerperium, each of which can simulate a neoplasm on clinical, gross, or microscopic examination.

Nonneoplastic—physiologic or reactive—conditions of the ovary may present as a mass lesion and mimic a malignant process clinically or radiologically and may result in a diagnostic dilemma on frozen section examination.