OBJECTIVE To examine the effects of an intermittent injection regimen of exogenous gonadotropin for controlled ovarian hyperstimulation on follicular development and on in vitro fertilization (IVF) outcome, 120 women who were candidates for IVF received intermittent injection (II) or consecutive injection (CI) regimens with a "short" protocol (SP) or a "long" protocol (LP) of gonadotropin releasing hormone agonist (GnRHa). Pure follicle stimulating hormone (pFSH) was injected to the women in the II groups on the first, second, and fifth days of the stimulation cycle and every other day thereafter. The women in the CI groups received a daily injection of pFSH. An additional 16 patients who were treated with both II-SP and CI-LP were also analyzed. RESULTS Although the cancellation rate in the II-LP group was higher than those in the other groups, follicular development and IVF outcomes in the II-SP group were similar to those in the CI groups. The number of injections in the II-SP group was about half that in the CI groups. CONCLUSIONS These results indicate that an intermittent pFSH injection regimen with a "short" protocol of GnRHa may be beneficial for patients in terms not only of being a less painful treatment but also causing less physical and mental stress than daily injections.