Information on ovarian metastasis of carcinoma of the extrahepatic bile ducts and gallbladder is limited. Sixteen examples are reported; 3 primary tumors were hilar cholangiocarcinomas, 5 common bile duct carcinomas, and 8 gallbladder carcinomas. The patients ranged from 21 to 87 years (mean, 59 years); 7 presented to gynecologists with nonspecific pelvic symptoms similar to primary ovarian neoplasms. The primary tumor was identified before the detection of the ovarian lesions in 5 cases, was simultaneously detected with the ovarian metastases in 9, and was diagnosed postoperatively in 2. All but one case had bilateral ovarian involvement. The thirty-one ovarian lesions included twenty-nine grossly abnormal ovaries that were enlarged (range, 3.0-16.5 cm, mean, 9.4 cm) and 2 ovaries with only microscopic involvement. The sectioned surface was solid in 9, solid-cystic in 15, and multicystic in 5. Microscopically, ovarian surface implants were seen in 66%, multinodular growth in 58%, and infiltrative stromal invasion in 81%. Mucinous epithelial differentiation was seen in 81%, sometimes with foci of benign-like or borderline-like epithelium simulating primary ovarian mucinous neoplasia. Cystadenoma and cystadenofibroma of nonmucinous type was even mimicked strikingly in some cases because of flattening of epithelium lining glands and cysts. Signet ring cells were present in sufficient quantity for a diagnosis of Krukenberg tumor in four tumors. Colloid-type carcinoma was observed at least focally in 3 tumors. Nonmucinous carcinomatous components included adenocarcinoma with high-grade endometrioid-like morphology in 2 cases, papillary adenocarcinoma simulating mixed müllerian epithelial adenocarcinoma in 1, and undifferentiated carcinoma in 2. Immunohistochemical studies in 8 cases showed a positive reaction for cytokeratin 7 in all and for cytokeratin 20 in 4 cases. The high rate of bilaterality, surface involvement, multinodular growth, and heterogeneity of patterns were the most helpful features for indicating a metastatic nature, with signet ring cells also being helpful in the minority of cases in which they were present. Although the diagnosis of a metastatic tumor to the ovary is possible in most of the cases based on standard diagnostic criteria, problems in the differential diagnosis may be posed by morphologic patterns that overlap strikingly with primary ovarian neoplasms, benign, borderline, and malignant, as discussed herein.