Pneumonia, which may be accompanied by the full spectrum of various clinical symptoms, with the most common including fever, chills, cough, chest pain, dyspnoea, tachypnoea, hypoxia, and auscultatory changes (crepitations, rales), is one of the most common lower respiratory infections. Chest radiography is a standard method used to confirm pneumonia. Transthoracic lung ultrasound has recently emerged as an alternative to radiology. The aim of this paper was to assess the utility of transthoracic lung ultrasound as an alternative to chest radiography in children with clinical manifestations of acute lower respiratory infection. A total of 63 patients aged between 1 month and 18 years, hospitalised in the Department of Paediatrics, Paediatric Nephrology and Allergology were qualified for the study. The study group included 44 children (mean age 4.3 ± 4.4 years), and the control group included 19 children (mean age 6.5 ± 3.8 years). Cough (42/44, 95%), dyspnoea (31/44, 70%), and fever (28/44, 64%) were the most common clinical symptoms in the study group. Auscultatory manifestations typical of pneumonia, i.e. crepitations, rales, reduced vesicular murmur, were observed in 30/44 (68%) patients; uncertain clinical symptoms of lower respiratory infection were observed in 14/44 (32%) patients. Lung ultrasound was performed within 48 hours of chest radiology. Both ultrasonographic and radiological lesions typical of pneumonia were found in 25/30 children presenting with clinical symptoms of pneumonia; no lesions in either of the modalities used were detected in 1/30 patients. Both ultrasonographic and radiological lesions typical of pneumonia were identified in 8/14 children with clinically uncertain pneumonia; no lesions were detected in diagnostic imaging in 1/14 children. Conclusions: Lung ultrasound is a useful tool for the assessment of lower respiratory inflammation in children. Ultrasonographic findings are comparable with those in radiology, which is considered a standard modality.