The investigators aim to investigate the effect of menstrual cessation in women with endometriosis treated with GnRH analogs for 6 months on bone mineral density and bone and muscle metabolism parameters and subsequently the effects of menstrual restoration after GnRH analogs discontinuation on the above measured parameters

Prospective, open-label, controlled 12month observational study Premenopausal women with surgically verified endometriosis will receive goserelin 1 injection per month for 6 months. Subsequently goserelin will be discontinued and patients will be monitored for another 6 months after menstrual restoration. Age- and BMI-matched premenopausal, health women will serve as controls. Controls will receive no treatment.