Uterine fibroids (myoma) are the most common benign tumor found in the female reproductive tract. A fibroid tumor is comprised of "swirls" of muscle fibers which are virtually identical to those making up the uterine wall. Fibroids vary widely in size, from those that can only be identified under a microscope to those the size of a basketball. Fibroid tumors constitute the most common indication for hysterectomy in the United States.