Objective: To compare the efficacy of two vaginal progesterone formulations, Crinone gel and Utrogestan capsules, for luteal phase support in blastocyst stage embryo transfers. Materials and Methods: We analyzed 460 consecutive cycles in patients undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI)–blastocyst transfer (BT) treatment at our institution between January 2004 and December 2007. Patients applied either Crinone 8% vaginal gel (90 mg, once daily) or Utrogestan vaginal capsules (200 mg, four times daily) for luteal supplementation. Progesterone was administered from the day of oocyte retrieval to pregnancy confirmation. Clinical pregnancy and implantation rates were the main outcome measures. Results: The clinical pregnancy rate (58.7% vs. 44.3%) and implantation rate (32.04% vs. 23.89%) were significantly higher in the Crinone group compared with the Utrogestan group after IVF/ICSI–BT treatment. Conclusion: Luteal phase support with Crinone 8% vaginal gel (90 mg daily) resulted in better clinical pregnancy and implantation rates than Utrogestan vaginal capsules (200 mg, 4 times daily) in IVF/ICSI–BT cycles.