Uterine leiomyomas and endometrial pathology are both associated with abnormal uterine bleeding. We report a case in which a nulliparous woman with heavy uterine bleeding and leiomyomas had undergone two prior hysteroscopic myomectomies for benign leiomyomas. She was evaluated, but was ineligible for a clinical trial of a novel Magnetic Resonance guided High Intensity Focused Ultrasound (MRgx200B;HIFU) device. The 8 cm, prolapsed submucosal leiomyoma hindered endometrial sampling and was inaccessible to HIFU treatment. Preoperatively, neither endometrial sampling nor saline sonohysterography was technically feasible. She underwent hysterectomy, and on histological examination of specimen, stage 1A grade 1 endometrial carcinoma was found on the endometrial side of the prolapsing fibroid. Endometrial pathology is an important consideration in the evaluation of abnormal uterine bleeding, even in women with large prolapsing leiomyoma.