Extrauterine mullerian adenosarcoma is a very rare tumor and it is characterized by a benign glandular component and a low-grade sarcomatous stromal component. These tumors have been reported to arise from ovarian or extraovarian endometriosis. However, there are scant reports on the MR findings of extrauterine mullerian adenosarcoma arising from deep pelvic endometriosis. We describe here a case of a large infiltrating extrauterine mullerian adenosarcoma arising from recurrent deep pelvic endometriosis and we discuss its MR findings.