Experience with ovulation induction treatment and understanding of the physiopathology of ovarian hyperstimulation syndrome (OHS), the risk factors and the clinical characteristics are of key importance for preventing and managing OHS. Light manifestations ofOHS are fairly common, occurring in up to a third of the cycles with superovulation induced by exogenous gonadotropins. A worsening of the symptoms of OHS can still normally be managed in out-patient form, but frequent monitoring and evaluation are essential. Serious disease resulting from OHS is much less common, but can involve risk to life. Hospitalisation might be necessary in some cases.