Background: Hypotonic fluids are widely used in pediatrics and are the standard of care when giving maintenance fluids. However, there are several reports of risk of iatrogenic hyponatremia attributed to this practice in the literature. There is therefore uncertainty as to whether isotonic fluids would be the more appropriate fluid. Objectives: The primary objective was to compare effects of hypotonic and isotonic maintenance fluids on plasma sodium levels in children between the ages of 2 months and 15 years admitted at Aga Khan University Hospital (AKUH). The secondary objective was to compare effects of hypotonic and isotonic maintenance fluids on other plasma electrolytes and need for additional fluid boluses in the same population of patients. Study design: Double blind randomized controlled trial of isotonic vs hypotonic maintenance intravenous fluids in children. Methods: One hundred and fifty two children with serum sodium levels between 130-150 mEq/L who required intravenous maintenance fluids were randomized to receive either 0.9% dextrose normal saline or hypotonic maintenance fluids as per normal practice. Hypotonic solution which was used in the control group, had sodium concentration between 20 and 100 mEq/L corresponding to 4mEq/Kg/24hr. Children aged between 2 months and 15 years requiring hospitalization at AKUH were eligible only when their physician prescribed intravenous maintenance fluid therapy. Patients with chronic or acute kidney failure/disease, at risk of cerebral edema (diabetic ketoacidosis or cranio- encephalic trauma), neonates (age <2month >old), sickle cell, with plasma sodium levels at hospital admission <130mEq/L or >150mEq/L, and/or cerebral malaria or severe malnutrition ( Z score <-3) and who refused to consent were excluded. Children were clinically monitored as per standard protocol. Blood electrolytes were obtained before commencement of v infusions to determine those eligible for inclusion and repeated after 24 hours or when fluids were stopped whichever was earlier. Any undesirable side effects were documented and managed as per standard practice. Primary outcome: Proportion of children with hyponatremia at 24hours after administration of maintenance fluids. Results: A total of 152 subjects were enrolled after obtaining informed consent. Of these, 78 and 74 were randomized to isotonic and hypotonic groups respectively. Overall, 25 (16.4%) patients dropped out of the study for various reasons. Hyponatremia occurred in 16.4% of the patients at 24 hours and a higher proportion of patients (23%) in the hypotonic group experienced hyponatremia compared to the isotonic group (10.3%) that was statistically significant (p = 0.03). The relative risk of