This study will compare bone mass in women with a history of endometriosis, a disease in which the lining of the uterus grows on nearby tissues, to that of women who have not had endometriosis. Endometriosis may be treated with medication or surgery, or both. Because uterine tissue grows more when estrogen levels are high, medical treatment is designed to lower estrogen. Decreased estrogen, however, is often associated with weak bones and hot flashes. Also, women with endometriosis may have lower bone density as a consequence of their disease. This study will look at bone density in these women, particularly to see if areas other than the lower back may be affected.

Regularly menstruating women between 40 and 50 years old, with or without a history of endometriosis, may be eligible for this study. Candidates are screened by telephone; women with endometriosis are asked to provide documentation of their endometriosis before beginning the study.

Study participants undergo the following tests and procedures:

• Medical history and blood sample collection
• Questionnaires about exercise activity, calcium intake, menstrual cycle history, cigarette use and medication history
• DEXA scan: This test evaluates the strength of the bones in the back, wrist, and hip. The DEXA scanner uses low-energy x-rays to determine bone density. Scans are done of the lower spine, upper thigh, hip, and the entire body. For the test, the subject lies on the scanning table. Each scan takes about 3 minutes, and the entire procedure may take as long as 1 hour.