Epithelial ovarian neoplasms can be divided into two major categories on the basis of their pathological and clinical behaviors: invasive ovarian tumors and borderline ovarian tumors. However, neither the etiology nor the pathogenesis of the borderline and invasive epithelial ovarian carcinomas has been understood completely. Borderline tumors are clearly more favaroble in terms of survival. The same pathological types can be seen both in borderline and invasive tumors. However; it is not clear if both diseases is a continuum of the same entity or are independent clinical entities. On the other hand, several in vivo and in vitro studies have demonstrated that overexpression of the cyclooxygenase-2 (COX-2) may have an important role in the development and the aggressive clinical behaviors of different malignancies. Furthermore, some recent studies have also revealed the overexpression of COX-2 in invasive epithelial ovarian carcinomas. In this manuscript, we propose that lower expressions of COX-2 may have a rote in the development of borderline ovarian neoplasias, whereas higher levels have a role in the invasive epithelial ovarian cancers and this may be the basis for the clinical difference of both entities.