Dedifferentiation is a process that may be found in metastasis from the neuroendocrine tumors. We present the case of a female within the seventh decade of life incidentally diagnosed with a mature teratoma with element of cartilages, bronchia, mucinous glands, and a poorly differentiated neuroendocrine carcinoma (Ki67 of 30%). After six months of chemotherapy and another six months of disease free interval, a metastasis of the great omentum was removed. The dedifferentiation was diagnosed based on much higher Ki67 (of 70%). The loss of estrogen receptor of 40% from the initial site to 3% into metastasis indicates an exclusive neuroendocrine aggressive pattern. The ovarian carcinoid is a rare situation, and metastasis to the great omentum with dedifferentiation is even seldom.