Hypernatremic dehydration in neonates is the most dangerous form of dehydration due to complications associated with it as well as its management. This study was planned to study the impact of the significant physiologic changes in body water content on serum sodium concentration in the immediate postnatal period and try to identify risk factors for hypernatremic dehydration. Material and Methods: Only healthy term/near-term babies were included. They were examined on day four of life in the

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... l baby clinic. These neonates were again examined on days seven and ten of life. Blood samples were collected on days four and ten of life, serum was separated and stored at -20°C. These serum samples were processed subsequently and serum sodium and potassium were estimated and compared with weight lost by the neonates. Results: 184 neonates were included in the study. Mean serum sodium level was 149 ± 6.0 mEq/l (range 135-172 mEq/l). Hypernatremia of varying severity was detected in 137 neonates. By day 10 of life sodium levels had normalized in all hypernatremic neonates except one, who was hospitalized on day 5 of life with hypernatremic dehydration. Perception of decreased milk production by mother, higher birth order, delivery by cesarean section and decreased urination in the neonate bore significant association with hypernatremia. Signs of dehydration were clinically discernible in nine patients and all of them had hypernatremia, however, most of the babies didn't have obvious dehydration signs and weight loss was comparable between two groups. Conclusion: Mild to moderate degree of hypernatremia is quite common during physiological dehydration in early neonatal period and adequate breastfeeding appears to be an effective and safe intervention for mild to moderate hypernatremic dehydration.