Preimplantation genetic diagnosis (PGD) is now being routinely used in many centers to prevent the birth of an affected child from couples with incurable genetic diseases resulting from single gene defects, chromosomal translocations, or aneuploidy. These couples are required to undergo in vitro fertilization (IVF) treatment. In routine IVF-PGD procedures, embryos are biopsied on day 3 post-insemination, genetic diagnosis is performed, and, if unaffected, biopsied embryos are transferred back into the patient on day 4 or 5. However, in some circumstances, freezing the embryos and analyzing them later to complete the PGD procedure cannot be avoided if the patient develops ovarian hyper stimulation syndrome (OHSS) or the PGD tests fail due to technical difficulties. In addition, some patients do not respond adequately to ovarian stimulation and produce only a few embryos in each cycle, requiring serial verification to obtain sufficient number of embryos for genetic analysis. Embryo freezing has been routinely used in IVF laboratories for decades and excellent post-thaw survival rates have been achieved. Safe use of embryos stored frozen for as long as 9 years to initiate a healthy pregnancy has been reported.