Aim Respiratory syncytial virus is the main pathogen responsible for bronchiolitis. Usually, there is no indication to perform diagnostic imaging or run laboratory tests in patients with bronchiolitis since the diagnosis is based on the clinical presentation. Chest radiogram can be useful in severe cases. So far, lung ultrasound has not been considered as an alternative in guidelines for imaging diagnosis of bronchiolitis. The aim of the study was to compare lung ultrasound and chest X-ray findings in children with bronchiolitis. Material and methods In our study we retrospectively compared diagnostic imaging findings in children with confirmed respiratory syncytial virus infection. The study included 23 children aged 2 weeks to 24 months and 3 children older than 24 months. Results Chest X-ray showed lesions in only 4 cases, whereas ultrasound abnormalities were found in 21 patients. Pathologies revealed by chest X-ray were the same for all 4 cases and consisted of an enlarged hilus and peribronchial cuffing. Sonographic lesions included inflammatory consolidations larger than 10 mm in 11 patients, small consolidations (<10 mm diameter) in 8 patients, interstitial syndromes in 6 patients, and alveolar-interstitial syndromes in 11 patients. A small amount of pleural effusion was detected in 3 patients. Conclusions Considering safety, short time of examination, high sensitivity in finding pleural effusion, small consolidations and signs of interstitial infiltrations, transthoracic lung ultrasound may be useful in the diagnosis of bronchiolitis.