Background: A viral upper airway infection usually precedes a viral lower airway infection, which is known as acute bronchiolitis. When children visit emergency rooms, this respiratory system illness is among the most prevalent ones. Lung ultrasonography (LUS) has been demonstrated to be a useful diagnostic method for a variety of cardiopulmonary conditions. Alternative diagnostic methods that do not include the use of ionising radiation should be considered during the examination of young individuals in order to lower their risk of cancer. Objective: This study aimed to compare the effectiveness of LUS, plain X-ray, and CT in diagnosing acute bronchiolitis and the degree of the illness in children. Patients and method: A single-centre comparative study included 53 infants aged less than 24 months admitted to the Pediatric Department (Benha University Hospital). All children were subjected to full medical history taking, clinical examination, plain chest X-ray, CT chest (performed prior to admission in infants experiencing respiratory distress in order to rule out COVID-19 infection), and LUS examination on admission. Results: In cases of severe bronchiolitis, chest US can accurately predict CT chest subpleural consolidation with a PPV of 72.22%, NPV of 100%, and accuracy of 90.57%. There was a significant agreement between the prevalence of subpleural consolidation between chest US and CT chest, with a kappa (κ) of 0.77. Regarding plain chest x-ray, 47 (89%) of the patients had bronchovascular markings (BVM), 23 (43.4%) had hyperinflation, and 3 (5.7%) had minimal subpleural consolidation. Conclusion: LUS as an initial diagnostic tool could lead to more safe, efficient, and cost-effective management of acute bronchiolitis in pediatric patients.