The most common secondary ovarian neoplasm to mimic an ovarian primary tumor is metastatic large intestinal adenocarcinoma. Even after histologic examination, metastases often are mistaken for primary adenocarcinomas, especially endometrioid carcinoma. We analyzed the clinical and pathologic features of 22 cases of documented large intestinal carcinoma metastatic to the ovary. Patients' ages ranged from 42 to 76 years. None of the intestinal primary tumors were Dukes stage A, 32% were Dukes B, and 68% were Dukes C. In nine patients (41%), the intestinal carcinomas had been resected previously from 4 to 60 months before removal of the ovarian metastases. Both ovaries were involved in 43% of the cases. Histologically, 19 cases were classified as pseudoendometrioid type, two as mucinous type, and one as mixed pseudoendometrioid-mucinous type. The most characteristic microscopic features of the ovarian metastases were garland and cribriform growth patterns, intraluminal "dirty" necrosis, segmental destruction of glands, and absence of squamous metaplasia. Special stains for mucosubstances were variable and not helpful in differential diagnosis. Immunohistochemical staining for carcinoembryonic antigen (CEA) was strongly positive. Recognition of these distinctive histologic features is crucial to proper identification of the intestinal origin of these ovarian tumors. Inappropriate treatment as primary ovarian carcinomas thereby is avoided, and more accurate assessment of prognosis is achieved.