This symposium on ovarian borderline tumors is based on the scientific program of the International Society of Gynecological Pathologists that was held in conjunction with the U.S.-Canadian Division of the International Academy of Pathology in March 1996. Four eminent gynecological pathologists who have had a special interest in these tumors were asked to focus on their more controversial aspects. The discussions reflect the enormous growth in our understanding of borderline tumors that has occurred over the past two decades but also reflect the lack of consensus regarding important aspects of nomenclature, histogenesis, and biology of the ovarian tumors and the extraovarian peritoneal lesions with which they are often associated. Dr. Silva, who organized the symposium, was hoping that an agreement could be reached among the participants. Although no consensus on the issues was attained, it is hoped that this symposium will highlight for the readers of the Journal the problem areas in borderline tumors while clarifying the various points of view held by the discussants.