BACKGROUND: Almost 800 women die every day due to complications in pregnancy and childbirth with hypertensive disorders in pregnancy accounting for 14% of cases. Research is focusing on prevention rather than treatment. There is evidence that indicates a role for micronutrients supplementation in preventing some pregnancy disorders. Low serum calcium level has been implicated in aetiopathogenesis of preeclampsia which led to the recommendation that calcium supplementation be given to women with reduced calcium level as part of the measure to prevent preeclampsia. A reduction in calcium in the diet may cause calcium depletion from all membrane storage sites, resulting in less stability of the vascular smooth muscle cell membrane. Calcium works in combination with other ions such as magnesium to provide an ionic balance to the vascular membrane, vasodilatation and resulting reduced blood pressure. Specifically, magnesium competes with sodium for binding sites on vascular smooth muscle cells, increases prostaglandin E, binds to potassium in a cooperative manner, and induces endothelial-dependent vasodilation and BP reduction. To date, studies on the serum Ca2+ and Mg2+ levels amongst women presenting with PE are conflicting and those on serum calcium-magnesium ratio are scanty globally and non-existent in the department of Obstetrics and Gynaecology of the University of Benin Teaching Hospital. It is therefore expedient to address this gap, with the aim of providing preliminary data that could influence the prevention and management of preeclampsia. AIM: This study aims to compare the serum calcium-magnesium ratio in women with PE and normotensive pregnant women. METHODOLOGY: This study was a case-control study conducted at the University of Benin Teaching Hospital, Benin City on 81 pregnant women of gestational age 20 weeks or more who were considered eligible based on set out criteria and comprised of 27 patients with preeclampsia and 54 normotensive women matched for age, gestational age and parity. Each woman had 5 ml of venous blood collected from them without stasis and analysed for serum calcium and magnesium and their ratio calculated and compared between groups.