Adenomyosis is a benign condition defined as growth of the endometrial glands and stroma deep into the myometrium. It is difficult to diagnose. It usually does not cause significant uterine enlargement. Here we present a case of third degree utero-vaginal prolapse with grossly enlarged uterus (24 weeks), the clinical and MR findings of which was mimicking sarcoma. Final diagnosis was established after hysterectomy based on histo-pathological features.