We present a compelling case of a 45-year-old female with a history of endometriosis and leiomyomas, who presented to her gynecologist with chronic pelvic pain complaints. Both a transvaginal ultrasound (US) and an MRI (magnetic resonance imaging) were ordered. The US demonstrated multiple uterine lesions, likely fibroids, and an endometrioma within the right ovary. The MRI of the pelvis with and without gadolinium identified a mass within the right ovary with homogenous intermediate T2-signal, restricted diffusion, and delayed enhancement relative to the myometrium. Several irregular-shaped lesions were also noted within the external myometrium, anterior pelvic wall, and the peritoneum, which were intermediate signal on T2-weighted images, restricted diffusion, and an enhancement pattern similar to the myometrium. The patient underwent a right adnexectomy. The histopathology findings were consistent with a low-grade endometrial stromal sarcoma (low grade-ESS) arising from the endometrial stroma of the right ovary. A debulking surgery confirmed the involvement of external myometrium, anterior pelvic wall, and the peritoneum secondary to a low-grade ESS without the endometrial cavity’s involvement. The underlying hypothesis is that the endometriosis stroma from extra-uterine structures such as the right ovary, pelvic and anterior peritoneum, and external myometrium may have subsequently resulted in a low-grade ESS. Low-grade extra-uterine ESS without endometrial involvement is a rare entity. Based on our literature search, this is one of the few reports covering the radiological features of low-grade extra-uterine ESS arising outside the uterus with a concomitant deep infiltrating endometriosis, but without the involvement of the endometrial cavity.Copyright © 2020 Elsevier Inc. All rights reserved.