Background. The aim of the study was to examine the effect of hyponatremia at admission as a negative prognostic factor in children hospitalized with COVID-19 pneumonia. Methods. The data of patients aged 1 month-18 years, who were followed with the diagnosis of pneumonia at Çanakkale Onsekiz Mart University Hospital, Department of Pediatrics, between January 2018 and May 2021 were examined, retrospectively. Patients (n=661) were divided into two main groups; COVID-19 pneumonia (n=158) and the other pneumonias [other viral pneumonia (n=161) and pneumonia of unknown etiology (n=342)]. Results. Six hundred and twenty-three patients with a median (Q1-Q3) age of 4 (1.5-8) years, 59.4% of whom were male were included in the study. The overall prevalence of hyponatremia at admission was 11.2% and was lower in those with COVID-19 pneumonia than in those with other viral pneumonia (6.4% vs. 15.2%, p=0.013). When evaluated irrespective of their COVID-19 status, hyponatremic patients had a higher supplemental oxygen requirement (OR 2.5 [1.4-4.3], p<0.001), higher need for intensive care unit (ICU) admission (OR 3.7 [1.3–10.2], p=0.009) and longer duration of hospitalization (p=0.016) than the normonatremic patients. In patients with COVID-19 pneumonia, being hyponatremic had no effect on supplemental oxygen requirements or the duration of hospitalization. When hyponatremic patients were evaluated, the supplemental oxygen requirements and duration of hospitalization of those with COVID-19 pneumonia were similar to the other pneumonias (p>0.05 for all comparisons). However, normonatremic COVID-19 pneumonias had higher supplemental oxygen requirements than other viral pneumonias and pneumonia of unknown etiology (OR 4.7 [2.2–10.3], p<0.001; OR 1.6 [1 –2.7], p=0.043, respectively). Conclusion. This study found that hyponatremia at admission is rarer in children with COVID-19 pneumonia than other viral pneumonias and has no effect on supplemental oxygen requirements or the duration of hospitalization.