Ovarian hyperstimulation syndrome (OHSS) is a potentially life-threatening complication during hormonal stimulation and ovulation induction with human chorionic gonadotropin (hCG) in the course of fertility treatment. Many pathophysiologic mechanisms are involved. A key mediator seems to be vascular epithelial growth factor (VEGF). In addition, patients with polycystic ovarian syndrome (PCOS), hyperandrogenemia or hypothalamic ovarian disorder seem to have an increased risk to develop the syndrome. Individual risk assessment and precautionary measures, such as low-dose stimulation, minimizing hCG doses for ovulation induction and even cancellation of embryo transfer, may help to reduce the incidence of the condition. Treatment of the more severe forms should include in-patient treatment, intravenous (IV) infusion therapy, fluid balancing, anticoagulation, and drainage of ascites. The rationale in reproductive medicine should be implicate a high baby-take home rate in combination with a low incidence of adverse effects.