Uterine leiomyomata (fibroids) are very common, benign tumors present in an estimated 30% of women in the US. They are a local proliferation of smooth muscle cells surrounded by a pseudocapsule. While they are often asymptomatic, symptoms may include pain, bleeding or pressure. Fewer than 1% ever progress to leiomyosarcoma. They are commonly found on ultrasound. They are not generally distinguishable from leiomyosarcomas other than by rate of growth. In the post-menopausal woman, they generally decrease in size or disappear. If a post-menopausal woman presents with an expanding mass in the uterus, malignancy would be strongly suspected.