This prospective study evaluated the frequency, etiological causes of children with hyponatremia (serum sodium< 135 mEq/L) in 500 children aged between 1 month and 14 years of age admitted at tertiary care hospital in Rajasthan, India. Hyponatremia was found in 37% (185/500). Meningitis/encephalitis accounted for 20.5% followed by pneumonia and acute diarrhea each accounting for 12.43% of cases. Other causes were septicemia (7.6%), seizure (7.6%), cardiac diseases (3.2%), renal diseases (5.3%), liver diseases (2.7%). This study shows hyponatremia occurs frequently in children requiring hospitalization and thus should be anticipated and given attention in management plan.