Summary. Previous studies have suggested that increased dietary calcium is associated with a decreased occurrence of pregnancy-induced hypertension. In this study 106 young healthy nulliparous women, residing in Quito, Ecuador, were enrolled in a double-blind, randomized, controlled clinical trial. From 24 weeks gestation until delivery they received either 2 g of elemental calcium per day or a placebo. Calcium supplementation was associated with a significantly decreased risk of pregnancy-induced hypertension, with 4.1% developing pregnancy-induced hypertension in the treatment group versus 27.9% in the placebo group. Treatment was associated with a decrease in both systolic and diastolic blood pressure over the course of pregnancy. In addition, there was a small but significant increase in serum ionized calcium levels in the calcium-supplemented group during the treatment period.