Severe preeclampsia (HELLP syndrome) is a life-threatening pregnancy complication, usually a severe form of preeclampsia. In this study, we aimed to examine histopathologic changes and Endothelin-1 and KI-67 expression levels by immunohistochemical methods in severe preeclamptic placentas. Severe preeclampsia and obstetric characteristics and biochemical and hematological characteristics of healthy subjects were compared. Placenta sections were stained with hematoxylin-eosin for histopathological examination. In the histopathological examination of severe preeclamptic placenta, degeneration in synaptic and cytotrophoblastic cells, increase in insidious knots, fibrinoid necrosis, degeneration in endothelial cells, calcification and hyaline villous stains were observed. In the severe preeclampsia group, Ki-67 expression increased in decidua cells and inflammatory cells, while endothelial cells in the vessel wall and inflammatory cells in the villus and intervillous spaces increased. It is thought that angiogenetic and cellular proliferation is induced in a co-ordinated manner and significantly influences fetal development.