Endometriosis is one of the most frequently encountered benign diseases in gynecology. Complete resolution of endometriosis is not yet possible, but therapy has essentially three main objectives: (1) to preserve and improve fertility, (2) to reduce pain, and (3) to delay recurrence for as long as possible. The aim of this paper is to focus on fertility preservation in women with severe endometriosis. In moderate and severe endometriosis, a medico-surgical approach remains the gold standard, but more and more papers are reporting a low ovarian reserve after laparoscopic cystectomy for endometriomas. Indeed, very frequently, normal ovarian tissue is excised together with the endometrioma wall. Ovarian surgery in endometriosis patients should therefore be performed by experienced surgeons in order to both preserve and improve fertility. Preservation of ovarian tissue should be considered in all patients at serious risk of future fertility impairment, particularly before any treatment likely to result in ovarian endometriosis recurrence and/or premature ovarian failure.