Purpose: Plastic surgeon can easily misdiagnose the mass on the postoperative scar as hypertrophic scar. We present a case of endometrioma at abdominal scar after cesarean section. Methods: A 36 year-old female visited with a protruding, rubbery hard mass on her abdominal scar. The mass grew slowly after cesarean section performed 7 years ago. She has felt intermittent pain, not with menstrual cycle, for 2 months. The ultrasonography showed a solid irregular, ill defined mass with heterogenous echogenicity. The MRI finding is suggestive of malignant soft tissue tumor with deep fascial invasion. Incisional biopsy showed acanthosis, melanophage, lymphoplasmacytic infiltration. So we excised mass elliptically, we could see chocolatelike discharge from the mass, adhering to external oblique muscle fascia. The mass confirmed histologically as an endometrioma. Results: The mass was completely removed and did not recurr. The patient does not complain more about pain or any discomfort. Conclusion: Plastic surgeons should be aware of the possibility of endometrioma when the patient present with mass on her abdominal scar after surgery of the pelvis and abdomen.