The 5-year survival for women with Stage-I borderline tumours (BOT) is favourable, about 95-97%, but the 10-year survival is only between 70 and 95%, caused by late recurrence. The 5-year survival for Stage II-III patients is 65-87%. Standard primary surgery includes bilateral SOEB, omentectomy, peritoneal washing and multiple biopsies. Second cytoreductive surgery is recommended for patients with recurrent disease. Adjuvant postoperative therapy is not indicated in Stage-I diploid tumors. Occasional responses to chemotherapy have been reported in advanced BOTs but no study has shown improved survival. Recently a new theory has been developed describing a subset of S-ovarian cyst adenomas that evolve through S-BOT to low-grade carcinoma. A more correct staging procedure, classification of true serous implants and agreement on the contribution to stage of the presence of gelatinous ascites in mucinous tumours may in the future change the distribution of stage and survival data by stage for women with BOT. Independent prognostic factors in patients with epithelial ovarian BOT without residual tumour after primary surgery are DNA-ploidy, international FIGO-stage, histologic type and patient age. Studies on other molecular markers have not yet uncovered a reliable prediction of biologic behaviour, however, there is hope that future studies of genetics and molecular biology of these tumours will lead to useful laboratory tests. Future questions to be addressed in this review include the following: Have patients with borderline tumours in general been over-treated and how should these patients be treated? How to define the high-risk patients? In which group of patients is fertility-sparing surgery advisable and, do patients with borderline tumours benefit from adjuvant treatment?