Hypertensive disorders of pregnancy is a major cause of fetal and maternal morbidity. Epidemiologic observations have shown an inverse association between calcium intake and incidence of eclampsia. Calcium supplementation has been reported to decrease blood pressure in pregnant women, although this remains controversial. The mechanism responsible for the effect of calcium on hypertinsion in pregnant women is unknown. This paper is a review of some of the recent calcium supplementation trials that have been carried out and their effectiveness in reducing systolic and diastolic blood pressure and decreasing the incidence of hypertensive disorders of pregnancy.