The most serious complication of ovarian stimulation for in vitro fertilization is severe ovarian hyperstimulation syndrome (OHSS), a rare but potentially life-threatening condition. The present review discusses the place of gonadotropin-releasing hormone antagonists (GnRH-ant) in primary, secondary, and tertiary prevention of OHSS. Sound evidence indicates that the routine use of GnRH-ant instead of GnRH agonists (GnRHa) during ovarian stimulation drastically reduces the relative risk of OHSS. GnRH-ant are therefore useful for primary OHSS prevention, and an increased use of antagonists should help reduce the overall incidence of severe OHSS with its associated risks and complications. In patients on antagonist protocols identified to be at risk of developing severe OHSS, replacing human chorionic gonadotropin with GnRHa as a trigger of final oocyte maturation has been proposed as an effective measure of secondary prevention. A concept of combining GnRHa triggering with cryopreservation of all oocytes or embryos has yielded promising results as far as total avoidance of OHSS is concerned while providing a good chance of pregnancy for the patient in later frozen-thawed embryo transfers. In patients with early onset of OHSS, reinitiation of GnRH-ant in the luteal phase as a measure of tertiary prevention might lead to rapid regression of the syndrome; however only limited data on this new concept are available in the literature.