Epidemiological and histological evidence (epidemiological, histological and molecular/genetic) linking endometriosis with the development of endometrioid and clear cell ovarian carcinoma in a small number of cases. There also exists an animal model in which a transition from spontaneously arising endometriosis to cancer can be elicited by means of genetic manipulation involving a small number of oncogenes and tumor suppressor genes. However, this model of transition from benign tissue to cancer has still not been fully confirmed in humans. All in all, the available evidence is still very controversial in many aspects, and is not enough for considering endometriosis a premalignant condition at the present time.