|Objective To report an efficacy of gonadotropin releasing hormone (GnRH) antagonist administration after freezing of all embryos for treatment of early type ovarian hyperstimulation syndrome (OHSS). Methods In 10 women who developed fulminant early type OHSS after freezing of all embryos, GnRH antagonist (cetrorelix 0.25 mg per day) was started at the time of hospitalization and continued for 2 to 4 days. Fluid therapy and drainage of ascites was performed as usual. Results Early type OHSS was successfully treated without any complication. At hospitalization, the median (95% confidence interval [CI]) of the right and the left ovarian diameter was 10.0 cm (7.6 to 12.9 cm) and 8.5 cm (7.5 to 12.6 cm). After completion of GnRH antagonist administration, it was decreased to 7.4 cm (6.2 to 10.7 cm) (P=0.028) and 7.8 cm (5.7 to 12.2 cm) (P=0.116), respectively. The median duration of hospital stay was 6 days (3 to 11 days). Trans-abdominal drainage of ascites was performed in 2 women and drainage of ascites by percutaneous indwelling catheter was performed in 4 women. No side effect of GnRH antagonist was noted. Conclusion GnRH antagonist administration appears to be safe and effective for women with fulminant early type OHSS after freezing all embryos. Optimal dose or duration of GnRH antagonist should be further determined.