The authors reviewed the clinical and pathologic features of 35 cases of secondary ovarian neoplasms in which the clinical presentation was that of a primary ovarian tumor. The most common secondary neoplasms to mimic an ovarian tumor were colonic adenocarcinoma, breast carcinoma, lymphoma, carcinoid, and gastric adenocarcinoma. It was found that a classification based on gross appearance was useful in evaluating these neoplasms. Solid neoplasms with either a diffuse or nodular gross appearance had distinct histologies so that accurate diagnosis was possible. Cystic neoplasms, especially colon adenocarcinomas, were deceptive and frequently misclassified as primary ovarian adenocarcinoma. Since all of the metastatic colonic carcinomas had mucus-containing cells, the main differential diagnosis was between metastatic colonic carcinoma and primary mucinous carcinoma of the ovary. The absence of a mucus-cell predominant pattern and the lack of transition from benign-appearing epithelium to malignant epithelium are two useful criteria in making this important distinction. Other features may also prove helpful.