Objective Malignant transformation in a dermoid cyst of the ovary is a rare complication, occurring in only 1-2% of cases, with squamous cell carcinoma being the most common type. Preoperative diagnosis is difficult because of the lack of specific symptoms and signs to suggest malignancy. Because of the small numbers of women involved, our knowledge of this rare tumour type is limited. This study aims to further characterise the population of women affected, the disease itself and the most appropriate management strategy.Design We identified 14 women with this diagnosis between 1989 and 2006. This is a descriptive study, looking at the patient characteristics, mode of presentation and the role of tumour markers and radiological imaging in diagnosis. We also examined the stage and pathological features of the tumour at presentation and the subsequent course of the disease. We have also described our experiences using surgery, chemotherapy and radiotherapy in the management of these women.Results We found that these tumours present at an age older than that of mature teratomas and that there are no reliable diagnostic tools or prognostic indicators. The behaviour of these tumours is unpredictable, and the role of chemotherapy and radiotherapy remains unclear. We suggest that repeated surgical resection of disease at the time of relapse could give a very durable response in selected women.