Mature cystic teratomas comprise of 10-20% of ovarian neoplasms. Malignant transformation in a dermoid cyst occurs in 0.17-2% of cases. Primary ovarian melanoma arising in a dermoid cyst is an extremely rare entity. It must be differentiated from a metastatic melanoma which is more common. A fifty nine year old female presented with lower abdominal pain and heaviness. A right adnexal mass was noted on Computed tomography (CT) scan. Left ovary and uterus were normal. She underwent a right salpingo-oopherectomy. Histopathological examination along with immunohistochemical analysis and clinical correlation serves the diagnostic purpose and surgery with adequate margin clearance plays an important role in management. We report a rare case of primary malignant melanoma arising in a mature cystic teratoma.