We describe the clinical and biological characteristics of 12 pregnant women with the HELLP syndrome as defined by Weinstein in 1982 (H for hemolysis, EL for elevated liver enzymes and LP for low platelet count). The data demonstrate that this syndrome is an obstetric emergency threatening the lives of both mother and child. However, if delivery is prompt the prognosis is good. The suspicion of gestosis requires a hematological assessment (complete blood count and close examination of blood film, evaluation of hemostasis) as an essential component in therapeutic decisions.