Ovarian serous tumors of low malignant potential ("borderline" serous tumors) are classified according to the histologic features of the primary ovarian tumor, without regard to any coexisting extraovarian disease. The peritoneal implants display a range of histologic appearances, ranging from benign glands (endosalpingiosis), to noninvasive papillary glandular proliferations resembling the ovarian neoplasms, to irregular glands associated with a desmoplastic stroma and having features of invasive disease. This review of 16 patients with histologically documented extraovarian tumor implants seen at Indiana University Medical Center, Indianapolis, and 13 patients whose tumor implants have been previously described in the literature indicates that the clinical stage of disease has much greater prognostic significance than does the implant histologic features. There is a tendency for patients with more advanced disease to have invasive implants. However, within a given clinical stage, disease progression or recurrence was not influenced by the presence or absence of invasive histologic characteristics in the tumor implants.