Growing evidence of successful outcomes achieved with the oocyte vitrification technique has greatly contributed to its application in the field of fertility preservation (FP). The population that can benefit from FP includes women at a risk of losing their ovarian function because of either iatrogenic causes or natural depletion of their ovarian reserve. Therefore, oncological patients and healthy women who wish to delay motherhood for various reasons—elective FP—are currently being offered this option. Satisfactory oocyte survival rates and clinical outcomes, including cumulative live birth rates, have been reported in recent years. These studies show that age at oocyte retrieval strongly affects reproductive prognosis after FP. Therefore, elective FP patients should be encouraged to decide before they reach the age of 35 years to significantly increase their chances of success. The effect of age has also been observed in patients with cancer and women diagnosed with endometriosis. The reproductive outcome after FP is worse in patients with cancer, but a direct association between the disease and reproductive outcome is yet to be proven. Young patients (≤35 years) with endometriosis who have undergone cystectomy before oocyte retrieval for FP have worse outcomes than nonoperated women in age-matched groups. In addition, the number of oocytes used per patient is closely related to success in all populations, with considerable improvement in the result with the addition of a few oocytes, especially in healthy young patients.