Objective: This study was undertaken to determine the pregnancy rate after transfer of cryopreserved blastocysts. Study design: Retrospective review of 61 patients from January 1, 2002, to December 31, 2003, who were transferred with blastocyst embryos cryopreserved on day 5 or 6 after culture in a sequential media. The cryopreserved blastocysts were thawed by using a 7- step dilution process after rapid thawing half hour to 2 hours before embryo transfer. Results: The pregnancy rate after transfer of 61 patients with cryopreserved blastocysts was 66% , with 49% having cardiac activity. The pregnancy rate after transfer of 3 blastocysts was 71% and after transfer of 2 blastocysts was 66% . The pregnancy rate of blastocysts cryopreserved after intracytoplasmic sperm injection was 56% . Conclusion: Cryopreservation and transfer of blastocysts appears to be a reliable procedure, and that the human blastocyst can be cryopreserved and thawed without a significant loss of viability. Study design: Retrospective review of 61 patients from January 1, 2002, to December 31, 2003, who were transferred with blastocyst embryos cryopreserved on day 5 or 6 after culture in a sequential media. The cryopreserved blastocysts were thawed by using a 7- step dilution process after rapid thawing half hour to 2 hours before embryo transfer. Results: The pregnancy rate after transfer of 61 patients with cryopreserved blastocysts was 66%, with 49 % of cardiac activity. The pregnancy rate after transfer of 3 blastocysts was 71% and after transfer of 2 blastocysts was 66%. The pregnancy rate of blastocysts cryopreserved after intracytoplasmic sperm injection was 56%. Conclusion: Cryopreservation and transfer of blastocysts appear to be a reliable procedure, and that the human blastocyst can be cryopreserved and thawed without a significant loss of viability.