Objective To compare IVF outcome in single versus two blastocyst transfer in good-prognosis patients. Design Retrospective data analysis. Setting University-based IVF practice. Patient(s) Assisted reproductive technology outcome was compared in 41 patients who underwent elective single blastocyst transfer and 66 patients who underwent two blastocyst transfer. Intervention(s) None. Main Outcome Measure(s) Implantation rates, clinical pregnancy rates, cumulative pregnancy rates, twin pregnancy rates. Result(s) Blastocyst cycles between January 2003 and August 2004 (n = 238) were reviewed. Criteria for elective single embryo transfer established by our clinic were applied retrospectively to blastocyst cycles. Patients who met the criteria were divided into two groups, those who underwent elective single embryo transfer (eSET) and those who underwent two embryo transfer (2ET). Patient and cycle characteristics were similar for both groups. There were no differences in implantation rate (76% vs. 66%) or pregnancy rate (76% vs. 79%) between the eSET and 2ET groups. There was a significant difference in the number of twin pregnancies (3.2% vs. 62%) in the eSET versus 2ET group. Cumulative pregnancy rates were found to be 83% for both groups. Conclusion(s) Single blastocyst transfer can be performed in good-prognosis patients without compromising pregnancy rates. Twin pregnancy rates can be significantly reduced with eSET.