Hyponatremia is one of the most common electrolyte disorders in hospitalized children. The underlying mechanisms are poorly understood and potentially multifactorial, making management difficult, particularly in neonates. This retrospective study aimed to determine the incidence and etiologies of hyponatremia in hospitalized children under the age of 100 days, in our pediatric tertiary care hospital over a 1-year period. The etiology of hyponatremia was determined by reviewing the data noted in each patient's medical reports. Neonatal hyponatremia had a prevalence of 4.3% (86/2012 patients) and was mostly hospital-acquired (74/86 patients). Fifty-nine patients (68.9%) were preterm neonates. The etiology was iatrogenic in 26 cases (30.2%). In other cases, hyponatremia was due to transient (23 patients, 26.7%) or genetic abnormalities of the renal mineralocorticoid pathway (3 patients, 3.4%), SIADH (12 patients, 14%), digestive disease (3 patients, 3.5%), acute renal failure (3 patients, 3.5%), or heart failure (1 patient, 1.2%).Conclusion: Our findings confirm that hyponatremia is a frequent electrolyte disorder in neonates. Various mechanisms underlie this condition, most of which could be prevented by optimized management. The prevalence of genetic hypoaldosteronism and pseudohypoaldosteronism was higher than expected. We provide a simple diagram to help physicians identify the mechanisms underlying neonatal hyponatremia. What is Known: • In neonates, hyponatremia may be multifactorial, making it difficult to treat. • Newborns display partial resistance to aldosterone, and preterms have a defect in aldosterone secretion. What is New: • Four percent of hospitalized neonates had hyponatremia, 86% hospital-acquired. Hyponatremia was due to a transient or constitutional defect of the mineralocorticoid pathway in 26/86 patients (30%) which is higher than expected. • We propose a tree diagram for improving the management of hyponatremia in neonates.