Survival rates after cancer have increased significantly in recent decades; however, these treatments also have drawbacks and patients (or parents in the case of children) must be informed of the long-term side effects of oncological treatments and the possible options for preserving the fertility of these patients. In oncological patients two special circumstances often arise: a short time to stimulate ovulation and the necessity of not reaching high estradiol levels. In applying embryo-freezing techniques to preserve the fertility of oncology patients, it is very important to know the couple's preference for the disposition of any unused embryos. Up to now, embryo cryopreservation has been the only clinically accepted method for preserving the fertility of oncology patients before they undergo chemotherapy and/or radiotherapy. The post-thawing pregnancy rates are acceptable and are around 30% per cryoreplacement depending on the number of embryos available and their quality.