We report a case of ovarian hyperstimulation induced by a GnRH agonist (Decapeptyl) in a patient aged of 23 years and having 3 years of primary infertility of male origin. Twelve days after agonist administration, several ovarian follicles, great-sized, and with a rate of elevated serum oestradiol have been noted. After triggering of the ovulation by 5000 IU of HCG, oocyte retrieval permitted the collection of 4 oocytes 3 of which were mature. Only one embryo with 4 cells has been transferred 48 hours after intracytoplasmic sperm injection fertilization (ICSI), but there was no pregnancy. Ovarian hyperstimulation induced by GnRH agonist is a rare event and only a few cases have been reported. The development of multiple follicles after the administration of an agonist is a paradoxal answer of the ovary to the pituitary desensitization without a clarified physto- pathology. The hypothesis of a direct action of the agonist on the ovary is likeliest. Triggering of ovulation by human chorionic gonadotrophin (HCG) has been achieved by certain authors. Fertilization of oocytes and transfers of embryos have succeeded in certain cases, but only one pregnancy has been reported that led to a living birth. We report a case of ovarian hyperstimulation induced by a GnRH agonist (Decapeptyl) in a patient aged of 23 years and having 3 years of primary infertility of male origin. Twelve days after agonist administration, several ovarian follicles, great-sized, and with After triggering of the ovulation by 5000 IU of HCG, oocyte retrieval permitted the collection of 4 oocytes 3 of which were mature. Only one embryo with 4 cells has been transferred 48 hours after intracytoplasmic sperm injection fertilization (ICSI), but there was no pregnancy. Ovarian hyperstimulation induced by GnRH agonist is a rare event and only a few cases have been reported. The development of multiple follicles after the administration of an agonist is a paradoxal answer of the ovary to the The hypothesis of a direct action of the agonist on the ovary is likeliest. Triggering of ovulation by human ch orilization gonadotrophin (HCG) has been achieved by certain authors. Fertilization of oocytes and transfers of embryos have succeeded in certain cases, but only one pregnancy has been reported that led to a living birth.