Pre-eclampsia, or pregnancy-induced hypertension, is a major cause of maternal and fetal morbidity and mortality complicating 7-10% of pregnancies. Although mechanisms underlying pre-eclampsia are not well understood, endothelial dysfunction is considered to underscore many of the pre-eclamptic manifestations including hypertension, proteinuria and edema. Leptin, the obese gene product from adipocytes, is produced by the placenta during pregnancy. Serum leptin levels are elevated under normal pregnancy especially during the second trimester, which rapidly decreases and returns to normal after delivery, indicating the role of leptin as a gestational hormone for energy balance. Recent studies have revealed that the placental production of leptin may be pathologically augmented under pre-eclampsia although conflicting data also have been reported. Nevertheless, hyperleptinemia and possible further augmentation under pre-eclampsia may predispose to the development of maternal leptin resistance, which may be a component of insulin resistance predisposing the onset of endothelial dysfunction. This review summarizes recent findings regarding the putative changes of serum leptin levels during pre-eclampsia and the potential consequences on the vascular system.