Introduction/Background Cystic teratoma is the most common ovarian neoplasm but the malignant form is very rare and it accounts for 1%. It consists of well-differentiated derivatives of germ cell layers (i.e., ectoderm, mesoderm, and endoderm) developing as hair, muscle, teeth, or bone.

Methodology 33-years old woman was admitted to our hospital because she noticed that her stomach had grown. She had occasional abdominal pain and constipation for several years. We did a detailed gynecological examination. Ultrasound examination with an abdominal probe showed that it was a tumor 15 cm in diameter, which consisted partly of hyper, partly hypoechoic content. The other blood parameters were within normal limits. Tumor marker Ca 125 was within normal limits as CEA, but the value of alpha-fetoproteins was elevated.

Results We decided to do a laparotomy and removed the tumor completely. We checked other internal genitals organs and they were unchanged. We took a biopsy of the other ovarium. Histopathological findings confirmed that it was a malignant teratoma. One month after the operation, the patient developed abdominal pain and an ultrasound showed a cyst on the other ovary. We performed a second laparotomy and the whole abdomen was with meta changes. We did hysterectomy, omentectomy, and oophorectomy. She received six cycles of chemotherapy but unfortunately, the patient died after 7 months of primary treatment.

Conclusion Although malignant teratoma is very rare caution should always be exercised in treating these tumors and the dilemma remains as to which is the best option in primary treatment as it is most often young women who want to preserve their fertility. Can elevated alpha-fetoprotein levels help us predict the potential malignant transformation of ovarian cystic teratomas?