BACKGROUND De novo malignancies have become one of the leading causes of late mortality after renal transplantation, with their incidence being 2-15 fold higher than in general population. We present herein a unique case of ovarian carcinosarcoma in a renal transplant recipient. METHODS A 69-year-old female renal transplant recipient presented with progressive distension and vague abdominal pain. Clinical examination revealed a large abdominal mass. Magnetic resonance imaging scan verified the presence of the mass. An exploratory laparotomy was performed, identifying a giant tumor measuring 33 x 22 x 10 cm. Optimal debulking surgery was performed, the postoperative course was uneventful and she was discharged on the 8(th) postoperative day. The final diagnosis was ovarian carcinosarcoma. The patient received adjuvant chemotherapy and at 6-month follow-up, she was disease-free. CONCLUSIONS Ovarian Carcinosarcoma is a rare and aggressive neoplasia, comprising 1-2 % of all ovarian tumors. Radical surgical approach, as well as appropriate chemotherapy are the cornerstone of treatment. In the presented case, where immunosuppression is involved, further evaluation should be made as far as immunosuppression dose reduction or switch is concerned.