Ovarian mucinous cystadenomas of borderline malignancy that contain foci of intestinal differentiation are well recognized. Borderline tumors lined by mucinous epithelium of endocervical type and characterized by papillae architecturally similar to those of serous borderline tumors, however, have not been described in the literature. We have studied 30 tumors of this type. The patients averaged 34 years of age. Forty percent of the tumors were synchronously bilateral and 30% were associated with endometriosis. Four tumors were complicated by peritoneal implants, one by both peritoneal implants and lymph node metastasis and one by lymph node metastasis alone. No patient had pseudomyxoma peritonei. Follow-up information was available on all the patients for a mean interval of 3.7 years. In two cases tumors developed in the conserved contralateral ovary; no deaths occurred. These tumors have important clinical and pathologic differences from mucinous borderline tumors with intestinal differentiation, but have many similarities to mixed-epithelial borderline tumors of Mullerian type.