Large cell neuroendocrine carcinoma (LCNC) of the ovary, or ovarian undifferentiated non-small cell carcinoma of neuroendocrine type, is a rare entity that is frequently associated with ovarian surface epithelial tumors. Few cases have been reported in the literature. LCNC is an aggressive tumor with tendency to present at advanced stages and to cause death after a short postoperative duration. We report three cases of LCNC diagnosed histopathologically. Immunohistochemically, the tumor cells were positive for chromogranin A, NSE, CD56, and pancytokeratin. The patients were treated postoperatively with combination chemotherapy. Due to the rarity of LCNC, the general consensus on standard therapy is not established. Although most patients are at stage I, the biological aggressiveness and poor prognosis of the tumors have been reported in previous reports despite extensive surgery and chemotherapy.