A 70-year-old woman presented with a 2-year history of increasing breathlessness. Computed tomography (CT) of the chest confirmed a well-defined cystic lesion abutting the mediastinum in the right hemi thorax measuring 8 × 6 cm. She underwent a right thoracotomy to excise the cystic lesion. Biopsies for histology demonstrated metastatic serous ovarian epithelial carcinoma. We report a very unusual primary presentation of ovarian epithelial carcinoma as a single cystic mediastinal mass. We also include a brief review of the literature.