Ovarian borderline tumors can show histologic features, such as different degrees of cellular proliferation, eosinophilic cells, autoimplants, and adenofibromatous architecture, the importance of which is not known. The aim of the study was to describe these features and correlate them with clinical characteristics. Eighty-three ovarian borderline tumors were studied for the aforementioned features. These were correlated with clinicopathologic features. Epithelial proliferation was associated with the T stage in serous tumors (P=0.0009), but not in mucinous tumors (P=0.97). It was positively associated with bilateral tumors (P=0.01) and the presence of autoimplants (P<0.0001). It was associated with the presence of eosinophilic cells, as tumors with extensive eosinophilic cells had a mean proliferation of 80.7%, for those with no such cells it was 23.8% (P<0.0001), and for those with a limited presence of eosinophilic cells it was 48.7% (P=0.03). Cellular proliferation was not associated with the size of the tumor. An adenofibromatous architecture was associated with unilateral tumors (P=0.02) and showed a trend (P=0.08) with regard to T stage in serous tumors. It was not associated with the size of the tumor. The presence of autoimplants was marginally associated (P=0.07) with bilateral tumors and it was not associated with the size of the tumor or the T stage. The presence of eosinophilic cells was not associated with the T stage, the size of the tumor, or bilateral tumors. The degree of epithelial proliferation, autoimplants, adenofibromatous architecture, and the presence of eosinophilic cells are important features in ovarian borderline tumors.