Undifferentiated carcinoma is rare tumors with the worst prognosis than any type of surface epithelial carcinoma. They are common in fourth and fifth decade. In most cases, these spread beyond the ovary at the time of diagnosis and cannot be optimally debulked. A 17 years unmarried girl presented with an ovarian tumor, which on ultrasonography measured 9.9 cm × 6.7 cm × 6.6 cm arising from the left ovary and extending into the pelvis. Right ovary and other organs were unremarkable. Lab investigations: S. alpha fetoprotein (S.AFP) – 0.85 (0.5–2 ng/ml), B – human chorionic gonadotropin – 1.2 (<5 mIU/ml), cancer antigen – 125–127 (35 units/ml), carcinoembryonic antigen – 3.26 (<2.5 ng/ml). At histology, the tumor had undergone extensive areas of necrosis. The focal viable areas showed a poorly differentiated aggressive tumor. Extensive inter‑observer variability in diagnosis existed. S.AFP levels were normal. AE1/AE3, EMA were positive while the rest IHC markers did not contribute to any specific diagnosis. The tumor was then diagnosed as undifferentiated carcinoma of the ovary. She received 3 cycles of cisplatin‑based chemotherapy postoperatively. Two months later, she developed a metastatic nodule near the umbilicus. She succumbed to her illness within 3 months of diagnosis.