Borderline ovarian tumors (BOT) consist of epithelial ovarian lesions that express cytological features of malignancy, but unlike malignant ovarian tumors, do not show obvious stromal invasion. The tumor incidence is between 1.8 and 4.8 per 100,000 females per year. The two major groups of BOT include serous BOT (S-BOT) and mucinous BOT (M-BOT). S-BOTs are divided into two categories: tumors limited to ovary and tumors spreading outside the ovary. M-BOTs are divided into two categories. The more common type is intestinal that constitutes 85% of cases and the second type is endocervical or Mullerian. Mullerian M-BOTs is bilateral in 40% of cases, while it is accompanied by pelvic endometriosis in 20-30% of patients. Microscopic examination by intraoperative frozen section is necessary because macroscopic view of ovarian tumors alone is not reliable. It is better to perform conservative surgery until the final report is ready in patients who wish to preserve their fertility. It is hard to differentiate them based on clinical characteristics. Values of tumor markers including CA125, CA19-9 and CEA in diagnosis of BOT are confirmed. Standard treatment of BOT is surgery as is the case with invasive epithelial ovarian cancer. In the majority of patients referred for BOT, since there is no suspicion of malignancy, staging is not performed. In these cases, making decision to repeat surgery and staging depend on factors such as the type of histology, abdominal exploration results in the previous surgery and probability of the presence of residual tumor.