When intra-uterine insemination (IUI) is chosen for the treatment of a mild sperm deficiency causing infertility or idiopathic (unexplained) infertility, there are a number of options for ovarian stimulation for these women who are usually ovulating spontaneously. There is now general agreement that for pure mild male factor infertility (sperm concentration 5-15 million/ml and/or progressive motility 20-32%), whether the ovaries are stimulated or not before IUI makes very little difference to the results. For unexplained infertility, it seems strange to stimulate more ovulations with gonadotrophins in a woman who is already ovulating but this is thought to be able to correct some undiscovered hormonal imbalance or increase the receptivity of the lining of the uterus (endometrium) enough to accept a pregnancy. Whatever the reason, stimulated cycles in combination with IUI are more effective than unstimulated cycles as regards pregnancy rates. The combination of IUI with stimulated cycles, although improving pregnancy rates, is often accompanied by unacceptable multiple pregnancy rates. With ovarian stimulation with gonadotrophins, the aim should be to achieve a maximum of two ovulations per cycle and this with strict criteria for administering hCG to trigger the ovulation, seems to give optimal results with minimal twinning rates.