Impaired endothelial barrier function resulting in increased vascular permeability is a characteristic vascular response in preeclampsia, a hypertensive and multiple systemic disorder of human pregnancy. During the last two decades, endothelial function in preeclampsia has been intensively studied and significant progress has been made in understanding the cellular and molecular bases of the altered endothelial cell response. In this review, we address the nature and mechanisms that are proposed to underlie the disturbed endothelial barrier function in preeclampsia and discuss the potential relevance of the endothelial cell responses to the initiation and/or progression of this vascular syndrome. Insights gained from the characterization of the endothelial cell phenotype assumed by the preeclamptic microvasculature may lead to novel therapeutic strategies for the management of this syndrome.