To determine the prevalence rate of subsequent development of ovarian cancer after excision of endometrioma.Retrospective cross-sectional study.University hospital.A total of 485 women with endometrioma.Excisions of endometrioma were performed between 1995 and 2004. Data were collected from medical records in 2013.Age, revised American Society for Reproductive Medicine score, cyst diameter, follow-up periods, endometrioma recurrence, and development of ovarian cancer.Recurrence of endometrioma was recorded in 121 patients (24.9% of the entire cohort), and 4 patients (0.8% of the entire cohort) developed ovarian cancer. All ovarian cancers developed from a recurrent endometrioma (3.3% of patients who experienced recurrence). Recurrence of endometrioma was significantly associated with ovarian cancer development.Ovarian cancers can develop after excision of endometrioma and are more likely to arise from recurrent endometrioma. Special care such as rigorous follow-up should be practiced to manage patients who experience recurrence of endometrioma.