A clinical practice guideline for the preservation of female fertility provides evidence-based recommendations for women at risk of irreversible ovarian failure due to gonadotoxic therapies for cancer and benign disease. It was developed by a multidisciplinary group following the WHO Guideline of nine Cochrane systematic reviews and GRADE evidence assessment, focusing on live births, pregnancy, time to pregnancy, delay in oncology and OHSS. If cancer treatment must be started within two weeks, a random-start stimulation protocol is conditionally approved to provide one extra mature oocyte. Concomitantly, letrozole is strongly recommended, which limits estradiol without reducing yield and reduces the risk of OHSS in hormone-sensitive tumors. For ovarian tissue cryopreservation, slow freezing and vitrification are equivalent; during chemotherapy, a concomitant GnRH-agonist is strongly recommended based on 17 RCTs, which improves live births. Oocyte cryopreservation is slightly preferred over tissue in sexually mature women for higher cumulative pregnancy and lower morbidity; fertility assessment combines age, AMH and AFC. Orthotopic transplantation is strongly preferred over heterotopic, and ovarian cortical fragments undergo routine histopathology with expanded tests for malignant cells.