Mature cystic teratoma of the ovary is the most common ovarian neoplasm (10%-20%). These tumors are generally benign but may undergo malignant transformation, 80% of which is squamous cell carcinoma, in postmenopausal women (1%-2%). Due to nonspecific findings, the preoperative diagnosis is challenging; most patients are detected at an advanced stage and have poor outcomes. A 40-year-old female, P2A0, complained of worsening lower abdominal pain and palpable abdominal mass. She had not been having menstrual periods for almost 4 months. For the last 3 months, she had asthenia, anorexia, and lost 10 kg. Abdominal examination was notable for an immobile, well-defined cystic mass measuring 12 × 8 × 8 cm with an irregular surface in the lower abdomen. Its overlying skin appeared reddish. A bimanual examination confirmed the adnexal origin of the cystic mass. Laboratory examination was notable for leukocytosis, thrombocytosis, increased neutrophil-to-lymphocyte ratio, and reduced absolute lymphocyte count. There was an increase in her cancer antigen 125. An abdominal ultrasonography examination showed bilateral mature cystic teratoma. A bilateral salpingo-oophorectomy was performed. A postoperative diagnosis of bilateral dermoid ovarian cysts was then established. The patient histopathology examination concluded squamous cell carcinoma (malignant transformation from benign cystic teratoma) in bilateral ovaries. The patient was referred to a gynecology oncology center for further examination and management. However, she missed the appointment for an unknown reason. The patient passed away 4 months after surgery. Clinicians should be aware of the possibility of malignant transformation of teratoma if a tumor has been present for a long time, its diameter is greater than 10 cm, there is a thickening of the cyst wall with papillary growth, there is an increase in tumor markers, and the patient is postmenopause. Malignant transformation of mature cystic teratoma remains a diagnostic and therapeutic puzzle and the prognosis is poor despite extensive initial surgery and optimal debulking.