Significant aberrations of serum calcium concentrations are frequently observed in the neonatal period. The flow of calcium ions from mother to fetus during 3 rd trimester of gestation to associated with chronic fetal hypercalcemia. At birth, the umbilical serum calcium level is elevated (10 to11 mg/dl) and serum calcium declines in the term babies for first 24 to 48 hours; nadir is usually 7.5 to 8.5 mg/dl. Thereafter calcium concentrations progressively rise to mean values observed in older children and adults. Early onset hypocalcaemia (during 1 st 3 days of life) is seen in preterm babies, low birth weight infants, infants of diabetic mothers and birth asphyxia. Late onset hypocalcaemia usually presents at the end of 1 st week but onset ranges from first days to several weeks after birth. It is classically seen in term infants fed high phosphate diets. Other etiologies include hypoparathyroidism, Magnesium deficiency and vitamin D deficiency. Vitamin D deficiency may be secondary to maternal vitamin D deficiency, malabsorption, Maternal anticonvulsant therapy, renal insufficiency and hepatobiliary disease. Human milk has a total antirachitic sterol content of only 25 to 50 IU/L which may be just enough to maintain the normal 25 hydroxy vitamin D [25 (OH) D 3] levels in term infants. Laboratory evaluations of vitamin D deficiency in newborns may reveal a low to normal serum calcium levels and low to normal phosphorus levels. Serum alkaline phosphatase is elevated and may invariantly be correlated with the disease severity. Treatment of vitamin D deficiency in neonates consists of initial doses of oral vitamin D 2 upto 5000 units/day, though higher doses may be required. Once the deficiency resolves, weaning off slowly of vitamin D 2 is advised. Frequent assay of ser um calcium level is necessary to avoid rebound hypervitaminosis D. Defects in vitamin D metabolism are treated with vitamin D analogues such as dihydrotachysterol and calcitriol. Oral calcium supplements may be necessary during high dose vitamin D therapy since serum calcium levels may drop precipitously as bones mineralize rapidly