In 3,972 human menopausal gonadotropin (hMG) and human chorionic gonadotropin (hCG)-stimulated menstrual cycles, severe ovarian hyperstimulation syndrome (SOHSS) developed in 10 patients (0.25%), while in 627 hMG-, hCG- and gonadotropin releasing hormone analog (GnRH-a)-stimulated cycles, 6 patients (0.95%) developed SOHSS. In cases of threatening SOHSS in the follicular phase (excessive estradiol values, multiple follicles), a preventive method was applied: follicular aspiration 12 hours after hCG administration and regular oocyte retrieval 36 hours after hCG (17 patients). The method of post-hCG aspiration in one ovary was effective, leading to the withdrawal of all signs of SOHSS within six days after the second aspiration. In hMG-stimulated, pretreated patients there were four deliveries of seven healthy infants (two singleton, one twin and one triplet), while one pregnancy in seven GnRH-a-stimulated and pretreated patients ended in a spontaneous abortion. Post-hCG aspiration is a quick, simple and effective method that prevents the development of SOHSS and permits pregnancy in the treated cycle. Although the pregnancy rate in patients who developed SOHSS was higher (100% per embryo transfer), one should also consider the high spontaneous abortion rate (33.3% for the hMG- and 50% for the GnRH-a/hMG-treated groups) and the fact that SOHSS is a life-threatening condition, demanding expensive, intensive care. According to our experience, post-hCG follicular aspiration is the treatment of choice in patients with signs of SOHSS.