Therapy of endometriosis with a GnRH-agonist (Leuprorelin) demonstrated a good therapeutical efficiency. As a side effect it had a significant negative impact on trabecular bone mass (non significant on cortical bone) as measured by DXA. Rising levels of Osteocalcin indicated the stimulation of bone remodelling. Three years after the end of the therapy a long term follow up control was able to detect the complete recovery of the mean density values in the extremities with even higher values in some patients compared with the initial measurement. In the spine half of the patients reached or surpassed the initial values. Regarding the patients history the differences in the recovery were obviously due to a different lifestyle especially body exercise, and not due to a different reaction to the GnRH-agonist therapy. Without being able to predict the individual bone loss due to a GnRH agonist therapy the results of this study indicate that the transient oestrogen deficiency does not result in a relevant long term bone loss or an elevated risk of osteoporosis. On the other hand in case of known risk factors or of a prolonged or repeated GnRH-agonist therapy the individual bone density and the individual bone loss should be controlled by DXA. Those patients with a significant negative impact on their bone mass then can be treated directly.