Clear cell carcinoma of ovary is uncommon ovarian tumour that arises from surface epithelium of ovary. It has well-known association with ovarian endometriosis. We report here the first case of bilateral clear cell carcinoma of ovaries in a 40-year-old woman with a 17-year history of bilateral ovarian endometriosis. In addition, during the longstanding duration of the endometriosis, the patient was treated with hormonal therapy, including oestrogen. It represents the first report of such bilateral involvement in the background of ovarian endometriosis. This should prompt clinicians to be aware that prolonged hormonal treatment of endometriosis may precipitate bilateral malignancy of the ovary.