One ovarian mucinous cystic tumor that contained a mural solid nodule of anaplastic carcinoma is described in a 35-year-old woman. The epithelial elements consisted of invasive well differentiated mucinous carcinoma. The anaplastic nodule showed some similarities with the cells described in sarcoma and sarcoma-like mural nodules. In favor of a diagnosis of anaplastic carcinoma there are poor circumscription of the nodules, vascular invasion and absence of a prominent inflammatory reaction.