Secondary tumors of the ovary (STO) are those neoplasms that spread to the ovary from extraovarian sites. Determining the primary versus secondary nature of an ovarian neoplasm may present the pathologist with little differential diagnostic dilemma in some cases, while in other cases there may be significant diagnostic challenge due to similarities in the gross, microscopic, and clinical features of some primary and secondary ovarian tumors. Adding to the diagnostic difficulty presented by the frequent overlap in morphologic and clinical features is the fact that, in some cases, the pathologist (and clinician) may be unaware of a synchronous or historical extraovarian primary neoplasm. As misdiagnosis impacts the expected prognosis of the tumor and may have an adverse impact on treatment, it is important that the pathologist has an appropriate index of suspicion regarding the possibility of metastasis and a grasp of the possible gross, microscopic, clinical, and immunohistochemical staining features of secondary ovarian tumors. Tumor metastatic to the ovary may originate from almost any primary site, especially in young females, in whom the rich vascularization of the ovaries may render them more susceptible to metastasis. As ovarian metastasis has been documented to appear many years after diagnosis of primary tumor originating from various extraovarian sites, it is emphasized that a history of neoplasia of any type, even if that history is remote, may be significant in the evaluation of an ovarian tumor with morphologic features unusual for an ovarian primary neoplasm.