Despite the fact that many methods have been proposed for the management of severe ovarian hyperstimulation syndrome (OHSS), its prevention is mainly achieved by withholding human chorionic gonadotrophin (HCG) administration and cycle cancellation. Currently no curative therapy is available. Three women diagnosed with polycystic ovarian syndrome underwent ovarian stimulation for IVF using a long gonadotrophin-releasing hormone (GnRH) agonist protocol. Six days after oocyte retrieval, severe early OHSS was diagnosed by analysis of haematocrit, white blood cell (WBC) count, serum urea, and ultrasonographic assessment of ovarian size and ascitic fluid. On the same day, antagonist administration was administrated and continued daily for 1 week, while resulting blastocysts were cryopreserved. Progression of severe early OHSS was inhibited in all three patients. A marked decrease of haematocrit, WBC, ascitic fluid, oestradiol, progesterone and ovarian volume was observed, during 1 week of follow-up suggesting a luteolytic effect of GnRH antagonist. None of the patients required hospitalization. In conclusion, GnRH antagonist administration combined with blastocyst cryopreservation 6 days post retrieval might represent a new approach for the effective management of patients with established severe OHSS. The flexibility of the approach allows the elongation of the monitoring period up to 8 days following HCG administration.