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Objective: To compare the efficacy of oocyte vitrification (OV) with that of ovarian cortex cryopreservation and transplantation (OCT) in women undergoing gonadotoxic treatments. Design: Prospective observational cohort study. Setting: Not applicable. Patient(s): Candidates for chemo-/radiotherapy who joined our fertility preservation (FP) program were included in this study between 2005 and 2015. One cohort included 1,024 patients undergoing OV; the other cohort included 800 patients undergoing OCT. Intervention(s): OV using the cryotop device and OCT using a slow freezing protocol. Main Outcome Measure(s): Live-birth rate (LBR) and clinical pregnancy rate (CPR). Result(s): Basal antimullerian hormone levels of the patients revealed no differences in ovarian reserve before FP (OV, 11.6 pM [5.4-24.7]; OCT, 11.8 pM [6.4-21.9]). In the OV cohort, 49 patients used the vitrified oocytes after a mean storage time of 3.9 years. In the OCT cohort, 44 sought pregnancy after a mean storage time of 5.5 years. A trend toward higher CPR and LBR (per patient) was observed in the OV group (risk ratio [RRCPR], 1.31 [95% confidence interval, 0.90-1.92]; RRLBR 1.39 [95% confidence interval, 0.95-2.03]), although differences were not statistically significant. In the OCT group, 46.7% of pregnancies occurred spontaneously and no pregnancy was achieved when the tissue was harvested beyond the age of 36 years. All patients except three undergoing OCT resumed or improved endocrine ovarian function. Conclusion(s): Although we observed a trend toward higher LBR after OV, OCT is a very effective method to preserve fertility, allows for natural pregnancy, and restores ovarian function. In clinical scenarios where OV is not feasible, OCT remains the FP technique of choice and should no longer be considered experimental. (C) 2017 by American Society for Reproductive Medicine.