OBJECTIVE: To determine the implantation rates of cryopreserved blastocysts using controlled E2 and P replacement cycles in women with functioning ovaries. DESIGN: Retrospective clinical study. SETTING: University teaching hospital. PATIENTS: Infertile women with cryopreserved blastocysts obtained from previous IVF attempts. INTERVENTIONS: Exogenous E2 was administered orally from cycle day 1 and P was started transvaginally from day 15. Blastocysts were transferred on the 5th day of endometrial exposure to P (day 19). MAIN OUTCOME MEASURES: Blastocyst implantation rate and pregnancy rate (PR). RESULTS: Ninety-eight percent of blastocysts survived thawing: 67 were transferred in 42 women. Eight pregnancies occurred giving a PR of 19% per ET and 11.9% per blastocyst. CONCLUSION: The high PR observed after transferring blastocysts on the 5th day of endometrial exposure to P in controlled E2 and P replacement cycles speaks for a forward slide of the window of transfer in case of blastocysts.