Sister Mary Joseph nodule is one of the less well-known signs of intra-abdominal metastatic disease. The primary tumor site is nearly always detected because of specific morphologic and immunohistochemical features of the umbilical tumor. We describe a case of a 74-year-old woman with a Sister Mary Joseph nodule, which appeared most likely to be metastatic from a primary serous papillary ovarian carcinoma based on the histologic examination and the immunohistochemical analysis. Despite an extensive workup, no primary tumor could be detected and therefore we ultimately diagnosed the tumor as an extraovarian carcinoma with primary site at the umbilicus. After a literature search we concluded that a primary adenocarcinoma of the umbilicus is extremely rare and to our knowledge has never been described with both morphologic and immunohistochemical features of a serous ovarian carcinoma.