Borderline tumors of the ovary are lesions that have certain abnormalities, particularly microscopic, common with cancers, nevertheless they are not cancer in the strict sense of the term. The diagnosis of this pathology requires a good expertise in anatomo-pathology because there are several histological variants that can modulate the therapeutic management. They can be located only on one or two ovaries but can also extend to the lymph nodes and/or the peritoneum. These tumors have a very good prognosis overall. The most important prognostic factors are: the stage, the type of peritoneal implants (less good prognosis in case of invasive implants in serous tumors) and the existence of a tumor remnant (in stages II or III). Treatment is primarily surgical. The reference surgery for ovarian tumours (in a patient no longer of childbearing age) is bilateral adnexectomy. However, this surgery must be conservative in a young woman in the case of a stage I or stage II/III tumour but without invasive implants. In case of tumor with peritoneal implants, surgical resection of peritoneal locations is the rule. In macroscopically limited ovarian stages, there is an indication to perform a peritoneal staging (cytology, multiple biopsies and omentectomy) in serous micropapillary forms. Treatment is in the vast majority of cases exclusively surgical (most often conservative - in order to preserve future fertility - in young patients). Indications for chemotherapy are rare. The only indications for chemotherapy are the presence of invasive peritoneal implants and certain forms of lymph node involvement. Follow-up is done on a regular basis, especially in the case of conservative treatment, and is based on a clinical examination, markers and imaging by abdomino-pelvic ultrasound (in patients who have had conservative treatment). Recurrences are not life-threatening since they usually occur in a borderline mode and therefore have a good prognosis. Surveillance beyond 10 years is required (especially after conservative treatment). This surveillance is then based on clinical examination, marker assay and imaging.