The prevention of ovarian hyperstimulation syndrome (OHSS) should be of paramount importance as it is by far the most serious complication of both ovulation induction and IVF. OHSS is an iatrogenic (physician inflicted) condition caused by overdosing with gonadotrophin stimulation and is therefore almost totally preventable. High responders to gonadotrophin stimulation are the group who are susceptible (age < 30 years, polycystic ovaries, lean body weight, previous cycle with a high response) as they will produce a large number of follicles which predispose to OHSS. Both anti-Mullerian hormone (AMH) and antral follicle count (AFC) have a high predictive value for the high responder and correlate well with each other. The secret of management for the high responder is to anticipate which women are likely to fall into this category and adjust the starting dose and stimulation protocol accordingly. In ovulation induction, only a chronic low-dose protocol should be used and for IVF, a GnRH antagonist protocol is preferred as this demands less gonadotrophins, is more patient friendly and allows the use of a one-shot GnRH agonist trigger of ovulation. This latter action, in place of the conventional trigger with human chorionic gonadotrophin (hCG), will prevent OHSS but needs strong following support in the second half of the cycle with progesterone and oestrogen medication or a very low one-off dose of hCG in order to maintain good pregnancy rates. Alternatively, and preferably, a ‘freeze-all’ policy, freezing all embryos to be replaced in a following natural cycle, will completely avoid OHSS and maintain good pregnancy rates.