We aimed to examine the behaviour of the angiogenetic factor vascular endothelial growth factor (VEGF) and its soluble receptor (sVEGFR-1) in polycystic ovary patients undergoing In vitro fertilisation (IVF) compared with respect to normally ovulating controls. Levels of VEGF and sVEGFR-1 were compared in follicular fluid and serum, both on the day of human choriogonadotropin (hCG) administration and on the day of oocyte retrieval (OR), in controls and polycystic ovarian syndrome (PCOS) patients undergoing IVF cycles. The bioactivity of VEGF (VEGF/sVEGFR-1 ratio) in the two groups was calculated. Thirty PCOS patients and 20 controls referring to the IVF Centre of the University of Pisa (Italy) were enrolled. In each patient, blood samples were collected on the day of hCG and on the day of OR administration, and follicular fluid samples. VEGF and sVEGFR-1 were measured by Enzyme Linked Immuno Sorbant Assay (ELISA). Serum VEGF bioactivity markedly increased in both groups after hCG administration. Serum and follicular fluid VEGF bioactivity was greater in PCOS patients than in controls on the day of OR. The increase in VEGF bioactivity in PCOS patients undergoing IVF was not only because of increasing levels of VEGF but also to decreasing levels of its soluble receptor. We believe that additional studies will clarify their role in the pathogenesis of ovarian hyperstimulation syndrome, which most often occurs in patients with PCOS.