There are four major hypertensive disorders complicating approximately 10% of all pregnancies. Preeclampsia classified as mild or severe refers to the new onset of hypertension and proteinuria after 20 weeks of gestation in a previously normotensive woman. Eclampsia, a variant of severe preeclampsia, refers to the development of grand mal seizures that should not be attributable to another cause. HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets) is also a severe form of preeclampsia. Chronic hypertension is defined as systolic pressure = 140 mm Hg, diastolic pressure = 90 mm Hg, or both, that antedates pregnancy, is present before the 20 weeks of pregnancy or persists longer than 12 weeks postpartum. Superimposed preeclampsia is diagnosed when a woman with preexisting hypertension develops new onset proteinuria after 20 weeks of gestation. Gestational hypertension refers to hypertension (usually mild) without proteinuria (or other signs of preeclampsia) developing in the latter part of pregnancy. it should resolve by 12 weeks postpartum. Preeclampsia is a syndrome characterized by maternal endothelial cell dysfunction. Oxidative stress, inflammation, circulatory maladaptation, as well as humoral, mineral, or metabolic abnormalities all appear to play a role in the pathogenesis of preeclampsia. Newer studies suggest that placental release of circulating factors that interfere with the action of vascular endothelial growth factor and placental growth factor plays a central role in its presentation. In this review, classification and pathophysiology of preeclampsia with its severe forms, eclampsia and HELLP syndrome, are discussed.