Background: Peritoneal effiusion is rare in malignant Brenner tumors and has been found in only 10% of patients.
Case: A 77-year-old woman presented with malignant Brenner tumor and ascites. The cytology of the ascitic fluid revealed many activated mesothelial cells intermingled with squamous tumoral cells. These cells were either isolated or arranged in small clusters. They were often round or oval with irregular and moderately hyperchromatic nuclei.
Conclusion: Presence of squamous cells in ascitic fluid associated with an ovarian tumor should raise the possible diagnosis of malignant Brenner tumor in addition to malignant transformed teratoma and secondary squamous carcinoma of the ovary.