OBJECTIVE We aimed to compare the efficacy of a gonadotropin-releasing hormone (GnRH) antagonist protocol and a GnRH agonist long protocol used in the first in vitro fertilization-embryo transfer (IVF-ET) cycle in an unspecified population of infertile couples. METHODS Fifty and 34 patients were treated with a GnRH agonist long protocol (agonist group) and GnRH antagonist protocol (antagonist group), respectively, in the first treatment cycle. The primary and secondary outcome measures were cumulative live birth rates after fresh and cryopreserved-thawed ETs and incidence of grades II and III ovarian hyperstimulation syndrome (OHSS), respectively. RESULTS No significant differences were observed in clinical pregnancy rates (38.0 vs. 32.4%) and live birth rates (22.0 vs. 23.5%), which included both fresh and cryopreserved-thawed ETs, between the 2 groups. However, the incidence of grade III OHSS was significantly lower with the GnRH antagonist protocol than the GnRH agonist long protocol. CONCLUSIONS Used in the first IVF-ET cycle in an unspecified population of infertile patients, the GnRH antagonist protocol showed the same clinical outcome as the GnRH agonist long protocol.