This retrospective case-control study was performed in an Academic centre for the diagnosis and treatment of endometriosis. It included patients with recurrent unilateral endometriomas who were previously operated for the same condition (cases) and patients without recurrency who previously underwent surgery for unilateral endometrioma (controls). The primary outcome of the study was to assess the impact on ovarian reserve of second surgery for recurrent unilateral endometriomas. The evaluation of ovarian reserve was performed by assessing serum anti-mullerian hormone (AMH) level, serum follicle-stimulating hormone (FSH) level, 17-beta estradiol level and antral follicle count (AFC).

Inclusion Criteria:

• reproductive age (at the time of both surgical procedures);
• two surgical procedures on the same ovary (stripping of endometrioma with
• largest diameter ≥ 4 cm; cases) performed at our Institution;
• one surgical procedures (stripping of endometrioma with largest diameter ≥ 4 cm; controls) performed at our Institution;
• histological diagnosis of ovarian endometriomas;
• complete assessment of ovarian reserve at routinary follow-up at our institution.

Exclusion Criteria:

• patients aged ≥ 40 years at the time of primary surgery;
• surgical procedures on the contralateral ovary (at primary or second-line surgery);
• previous salpingectomy or hysterectomy;
• unilateral ovariectomy at the time of first or second surgery;
• ultrasonographic diagnosis of persistent endometrioma after first surgery;
• additional surgical procedures for endometriomas or for other ovarian diseases before first surgery and between first and second surgery;
• hormonal treatment within 3 months from ovarian reserve assessment;
• patients followed-up < 3 months after second-line surgery (for cases).
• pregnancy and/or breastfeeding during the study period.

In this study were recruited women referred to an academic centre for the diagnosis and treatment of endometriosis.

Cases were patients undergoing second surgery for recurrent unilateral endometrioma.

Controls were patients previously operated for unilateral endometrioma.