The study aims to evaluate whether serum vascular endothelial growth factor (VEGF) levels, before treatment with gonadotropins, may be considered a predictive marker of moderate ovarian hyperstimulation syndrome (OHSS). At the University of Pisa hospital infertility unit we have retrospectively selected 10 patients who developed moderate forms of OHSS and 30 control patients who presented a normal response to ovarian stimulation among 400 women undergoing in vitro fertilization (IVF). Serum samples were collected before starting pFSH administration (150-300 IU/day). VEGF levels in serum were measured. No statistically significant difference was found between the serum VEGF levels of patients who developed moderate forms of OHSS and women without any symptoms of the syndrome. Further, serum VEGF concentrations were not significantly correlated with the age of the patients, the number of international units of FSH administered during the cycle of stimulation, the follicle and oocyte numbers counted on the day of the egg retrieval or estradiol levels detected on the same day. This study demonstrates that serum VEGF levels, before starting gonadotropin treatment, are not predictive of the subsequent development of moderate forms of ovarian hyperstimulation syndrome.