Objective Most Brenner tumors are benign, with only 1% being malignant. In this study we report on 13 cases with malignant Brenner tumor of the ovary and discuss the clinical, demographic and histologic features. Method Thirteen patients with malignant Brenner tumor of the ovary who were treated at Selçuk University Gynecology Department over a 6-year period from January 2004 to December 2010 were retrospectively analysed from hospital electronic medical records. Clinical and pathologic findings were reported. Results The median age of the study population was 55.69 ± 11.81 years (range 43-79 years). Most of the patients presented with abdominal pain (6/13, 46.2%). The mean size of the ovarian tumors was 9.19 ± 1.34 cm (range 4-16.5 cm). Six patients (46.2%) were in stage III, five (38.5%) in stage I, and two (15.4%) in stage IV. Ten patients (76.9%) received chemotherapy. The mean followup was 38.38 ± 23.25 months (range 5-84 months). During follow-up, recurrence was detected in 7 patients (53.8%). The mean recurrence time was 23.8 ± 14.46 months (range 11-48 months). Conclusion In our study, we found that diagnosis was at an advanced stage, and recurrence rate was high. The mainstay of treatment is surgical resection, but the exact regimen and benefit of adjuvant therapy remain unknown. © Japan Society of Clinical Oncology 2012.