Introduction/Background Immature teratoma is also known as malignant teratoma or teratoblastoma or Embryonal teratoma and includes less than 1% of all teratomas and one third of malignant teratomas. The tumor is uncommon during pregnancy. The aim of this report is to introduce a case of immature teratoma of the ovary diagnosed after normal delivery.

Methodology The patient was a 26 years old woman who had undergone surgery two years ago due to bilateral ovarian cyst and abdominal pain, and the pathology reported the mature cystic teratoma. The patient again referred due to enlarged abdomen following normal delivery. Laparotomy was performed due to large ovarian mass, and salpingo-oopherectomy was performed with report of immature teratoma in frozen section. After the surgery, the patient received four courses of BEP-regimen chemotherapy. Now, the patient is followed-up and tumor markers, sonography and examination of the patient are normal.

Results Given the rare nature of the disease and the importance of early diagnosis of malignant ovarian masses in order to increase the patients’ survival rate, it is necessary to pay more attention to the adnexa in ultrasonography and clinical examinations of pregnant women.

Conclusion Given the rare nature of the disease and the importance of early diagnosis of malignant ovarian masses in order to increase the patients’ survival rate, it is necessary to pay more attention to the adnexa in ultrasonography and clinical examinations of pregnant women.