Studies focusing on serum sodium disorders in children with community-acquired-pneumonia (CAP) are nearly entirely lacking, though clinical experience suggests that at least hyponatremia (HN) might be rather common. We evaluated the incidence of hypo- and hypernatremia, in relation to other clinical, laboratory and etiological findings, in pediatric CAP. Serum sodium concentration was measured in 108 ambulatory and hospitalized children with radiologically confirmed CAP of variable severity. The etiology of CAP was revealed by serology in 97 patients. HN (serum sodium < 135 mmol/l) was present in 49 (45.4%) children, and it was mild (> 130 mmol/l) in 92% of the cases. On admission, hyponatremic patients had higher body temperature (38.96 degrees C vs 38.45 degrees C, P = 0.008), white blood cell count (21,074/microl vs 16,592/microl, P = 0.008), neutrophil percentage (78.93% vs 69.33%, P = 0.0001), serum C-reactive protein (168.27 mg/l vs 104.75 mg/l, P = 0.014), and serum procalcitonin (22.35 ng/ml vs 6.87 ng/ml, P = 0.0001), and lower calculated osmolality (263.39 mosmol/l vs 272.84 mosmol/l, P = 0.0001) than normonatremic ones. No association was found with plasma glucose, type of radiological consolidation or etiology of CAP. HN is common but usually mild in children with CAP. HN seems to be associated with the severity of CAP, assessed by fever, need of hospitalization and serum non-specific inflammatory markers.