 After peaking in the third decade, bone mineral density BMD decreases slowly over time, with a more dramatic short-term decline at the time of menopause. Because of the association with osteoporosis and fracture, evaluation of BMD at the time of menopause is recommended, as is identification and treatment of any reversible causes of bone mineral loss. Most studies of women with endometriosis have shown no change or decreased BMD, while rats with induced endometriosis had a marked decrease in BMD. Often, studies in women did not control for factors that are known to affect bone density such as body mass index BMI, exercise, or calcium intake. To address the question of whether endometriosis is associated with a change in BMD, we previously matched healthy volunteers and endometriosis patients for age, race, BMI, exercise level and calcium intake and compared BMD in the two groups. We found a decrease in BMD in women aged 40 - 50 who had a history of endometriosis, in comparison to women who did not have such a history. This study will expand that experience by studying more women aged 40 - 50 years with a history of endometriosis and matching them to women of the same race with similar age and BMI, who do not have a history of endometriosis. Participants will fill out a questionnaire about their medical, exercise and dietary history and will provide a single blood sample. A bone density study will be done and results will be made available to the participants. 