Aim: Squamous cell carcinoma arising in a mature cystic teratoma is an extremely rare event. This effort aims at adding authors__ampersandsignrsquo; experience to the pool of knowledge of this very rare but ominous tumour. Case Report: Herein, we report a case of squamous cell carcinoma in mature cystic teratoma of right ovary in a 45-year-old woman presenting with abdominal mass which was diagnosed after surgery. The tumour was large and cystic. An exhaustive search was made to rule out the possibility of metastasis into the ovary. Discussion: Benign or malignant tumours that arise in a benign cystic teratoma are rare. Malignant transformation occurs in only 1-3% of benign cystic teratomas1, 2, 3. Preoperative diagnosis is difficult because of the lack of specific symptoms and signs to suggest malignancy 4. Factors such as age, tumour size, tumour markers and tumour imaging characteristics help in preoperative risk assessment. Better understanding of the pathology and prognostic factors of this group of tumours is required for early and proper management. Conclusion: This report emphasizes on the sinister nature of malignant transformation of mature teratoma and the importance of comprehensive investigations for early diagnosis and treatment.