Endometriosis is a chronic disease that affects women of reproductive age. Malignant transformation in endometriosis is considered to be an unusual event, only occurring in 0.7–0.1% of cases. However the association between endometriosis and endometrial cancer is not well defined. Also in literature, rare cases of uterine sarcoma, about 3% of all uterine malignancies, associated with endometriosis have been reported. The authors report a case of a 47-years-old Italian woman with histologic diagnosis of endometrioid ovarian carcinoma arising from endometriosis, endometrioid endometrial carcinoma, and undifferentiated endometrial sarcoma. Therefore there have been few studies addressing the relationship between endometrial stromal sarcomas (ESS), and endometriosis. Novel scientific findings are necessary to investigate a possible common pathway and an effective treatment, although complete tumor resection can reduce the recurrence rate.