AbstractBackgroundBronchiolitis is the most common acute viral infection of the lower respiratory tract in infants. Clinical severity is associated with different risk factors; however, no clinical, laboratory, or radiological findings are able to predict the course of the disease in full‐term infants. Lung ultrasound (LUS) is a valid technique for the diagnosis and evaluation of pediatric respiratory diseases.AimsThe aim of our study was to correlate an LUS score with a clinical score, to describe lung ultrasound findings in cases and controls, and to compare LUS findings with chest X‐ray (CXR) in infants hospitalized with bronchiolitis.MethodsWe conducted a single‐center, longitudinal, prospective study on 92 infants. Sixty‐three out of 92 infants were hospitalized for acute bronchiolitis (cases) and twenty‐nine out of 92 for diseases not involving the respiratory system (controls). All patients with bronchiolitis underwent a clinical evaluation with the assignment of a clinical severity score and performed lung ultrasound with the assignment of an LUS score. Twenty‐three out of 63 infants with bronchiolitis underwent also a CXR for clinical indications. Control infants performed only LUS.ResultsIn infants with bronchiolitis LUS score showed a positive correlation with the clinical score (r = .62, p < .001) and the length of hospitalization (r = .42; p < .001). The need of oxygen therapy was more frequent in the patients with higher LUS score (p < .001). LUS findings observed in the cases were the presence of B‐lines, subpleural consolidations, and abnormalities of the pleural line. No LUS alterations were observed in the controls. In patients who performed LUS and CXR, we found a correlation between the presence of abnormalities of the pleural line with LUS and the presence of air trapping with CXR (r = .55; p = .007).