Venous blood was obtained from 100 consecutive and unselected Saudi Arabian mothers and their neonates within 48 h after delivery. Plasma levels of 25-hydroxyvitamin D (25-OHD) and total calcium were measured in paired samples. Fifty-nine mothers and 70 neonates had subnormal (less than 10 ng/ml) 25-OHD levels. Plasma Ca concentrations were low in 61% of the mothers and 59% of the newborns consisting of 10 preterm and 38 full term babies. There were significant correlation between the plasma levels of maternal and neonatal 25-OHD (r = 0.54; P = 0.0001), maternal 25-OHD and Ca (r = −0.22; P = 0.03), neonatal 25-OHD and Ca (r = −0.28; P = 0.0009), and maternal and neonatal calcium levels (r = 0.46; P = 0.0001). Nevertheless, maternal 25-OHD was not invariably higher than that in the infant. Normocalcemia was observed in 29 neonates and 26 mothers (20 mother/baby pairs) in the presence of subnormal maternal 25-OHD. Twenty babies and 16 mothers including nine mother/baby pairs had hypocalcemia in the presence of normal levels of 25-OHD. This indicates that vitamin D plays a crucial, but not exclusive, role in calcium homeostasis during pregnancy.This study revealed that vitamin D deficiency is very prevalent during pregnancy in Saudi Arabia. It also showed that asymptomatic hypocalcemia in full term babies is far commoner than is generally appreciated. It is considered that vitamin D deficiency is primarily due to lack of exposure to sunlight. Encouragement to obtain sunlight exposure and fortification of food are the only alternative measures.