Metastatic mucinous carcinomas in the ovary are readily recognized when they show characteristic features, including bilateral involvement, only moderate tumor size, surface and superficial cortical involvement, nodular growth, and an infiltrative pattern. However, it is well established that some metastatic mucinous carcinomas can simulate primary ovarian mucinous tumors grossly and microscopically. Metastatic pancreaticobiliary tract adenocarcinomas present a particular diagnostic challenge due to their ability to exhibit borderline-like and cystadenomatous growth patterns, which can be misinterpreted as underlying primary ovarian precursor tumors and can be erroneously used to support interpretation of the carcinomatous components as arising from these purported precursors within the ovary. Thirty-five cases of metastatic pancreaticobiliary tract adenocarcinomas were analyzed. The mean patient age was 58 years (median, 59 y; range, 33 to 78 y). In 15 cases (43%), the pancreaticobiliary tract and ovarian tumors presented synchronously and in 2 cases (6%) the ovarian tumors presented earlier as the first manifestation of the disease. Ovarian tumors were bilateral in 31 cases (89%). Mean and median tumor sizes were 10.6 and 9.5 cm, respectively (range, 2.5 to 21.0 cm). Nodularity was present in 22 cases (63%) and surface involvement was identified in 14 cases (40%). An infiltrative growth pattern was present at least focally in 28 cases (80%), accompanied by borderline-like and/or cystadenomatous areas in 17 (49%) cases and as the exclusive pattern in 11 cases (31%). Conversely, borderline-like and cystadenomatous patterns were identified in 24 cases (69%) and as the exclusive patterns (either pure or combined with one another) in 7 cases (20%). Dpc4 expression was lost in 20 of 33 tumors analyzed (61%). Of 25 patients with follow-up, 23 patients had died of disease (mean/median time, 9/6 mo; range, 1 to 39) and 2 patients were alive with disease (at 1 and 25 mo). Frequent bilateral ovarian involvement, moderate tumor size, nodularity, and infiltrative patterns are useful features for identifying these ovarian tumors as metastatic. However, many tumors exhibit borderline-like and cystadenomatous patterns that, when dominant and combined with synchronous presentation, make recognition as metastases an ongoing challenge. Loss of Dpc4 expression provides the most useful immunohistochemical evidence for establishing the pancreaticobiliary tract as the most likely source of these metastatic mucinous carcinomas in the ovary.