Preeclampsia, a common complications of pregnancy, is associated with an increase in the concentration of leptin in the maternal blood, which precedes the clinical onset of the disease. This review addresses the potential sources of leptin and considers the possible consequences, although at present these are entirely conjectural. The placenta is likely to contribute to the rise in leptin, and placental hypoxia and inflammatory mediators may be important stimuli. The possible protective and damaging sequelae of an increase in the maternal leptin concentrations may range from beneficial stimulation of fetal growth to an increase in blood pressure through stimulation of sympathetic activity. Further research is needed to determine if the rise in leptin plays a role in preeclampsia or whether it is a secondary and unrelated bystander.