The definition of borderline ovarian tumors is pathological. It is based on the combination of several histological criteria established by Hart and Norris and reviewed by Scully et al. : pluristratification and epithelial budding, increased mitotic activity which can be very variable, cytonuclear atypia (differential diagnosis with benign tumors), absence of stromal invasion (differential diagnosis of malignant tumors). Serous tumors represent approximately 55% of borderline tumors. They are bilateral in 28-50% of cases. This histological type is, however, more often associated with extra-ovarian locations, as found in 30% of cases on average peritoneal implants whose detection is fundamental because the class tumor stage III. These can be invasive or non-invasive, the prognostic value of invasiveness is controversial. Pre and intraoperative diagnosis of borderline ovarian tumors is difficult and requires a multidisciplinary approach, involving surgeons, pathologists, radiologists and medical oncologists trained as much as possible with this type of lesion border. Staging should be as complete as possible and should be as far as possible during the initial surgical resection. A restaging should be made when the initial staging is incomplete. Restaging does not affect patient survival but used to evaluate the prognosis of the initial tumor. Its indication still remains controversial: it is recommended for early-stage tumors, for which the treatment is now well codified. The authors discuss the issue of keeping the ovaries during hysterectomy for benign lesions throught the case of a patient of 50 years who benefited 9 years ago a subtotal hysterectomy for polymyomatous uterus and presented a bilateral serous tumor borderline on remaining ovary.