Studies show that in half of all women, pieces of the inner lining of the uterus grow outside the uterus after menstruation each month. In severe cases, the tissue spreads over the ovaries and fallopian tubes. Called endometriosis, this condition can cause severe pain during menstruation and intercourse.

Once labeled the "working woman's disease," endometriosis is now known to affect 12 million American women-approximately 10 percent of the female adult population-from all walks of life. Endometriosis is estimated to occur in about 10 to 15 percent of menstruating women between the ages of 25 and 44; it can also occur in teenagers. Exactly how many women have this disease is unknown because it usually can be diagnosed only by direct-viewing, typically during surgery. As many as 25 to 50 percent of infertile women may have endometriosis, which can physically interfere with conception. Many women fail to seek medical help because they mistake the symptoms of this disease for normal menstrual discomfort.

Endometriosis can run in families and is more common in first-degree relatives (mother, sister, daughter) of women who have the disease than in other women. Other factors that increase the risk of endometriosis include giving birth for the first time after age 30, being of Caucasian descent, and having an abnormal uterus.