This retrospective study was undertaken to determine the value of blastocyst culture and transfer as a tool in assisted reproductive technology. Six hundred and fifty-five cycles in patients undergoing IVF treatment for infertility were involved. All patients were aged < 40 years. Day-2 embryos were transferred to 427 (group 1) and day-6 embryos (blastocysts) were transferred to 228 patients (group 2). Pronucleate oocytes obtained from IVF were cultured in vitro for 2 or 6 days. One to five embryos were transferred. A total of 10,146 oocytes were retrieved, 6,105 oocytes were fertilized, 2,222 embryos were transferred and 197 clinical pregnancies were achieved in all groups. Blastocystes were transferred to almost 90% of group 2 patients. The pregnancy rate per cycle and implantation rate per transferred embryo was 42.1% and 19.4%, respectively, in the blastocyst group compared to 23.6% and 8.6%, respectively, when embryos were transferred on day 2. Even though in the blastocyst group there was an increased number of oocytes fertilized at the same time there was a significant reduction in the number of embryos being replaced (3.2 vs 3.8). This study demonstrate that transfer of blastocysts increases the success of IVF when compared with day-2 transfers and reduces the number of embryos to be transferred.