Considering the recurrent exacerbation of children with CF and frequent radiation exposure, thoracic ultrasound (US) might be a useful tool for evaluation of pulmonary changes. An observational study included twenty-one CF patients admitted in acute exacerbation, for one year period. Ultrasound was performed using a convex 3–5 MHz probe; specific US features were used for normal lung and detection of consolidation, interstitial syndrome, pleural effusion or emphysema. CT was used as a gold standard for evaluation of pulmonary structural changes, after US examination. In five cases US features specific for consolidation were found (12.2% associating pleural effusion, emphysema and alveoli-interstitial syndrome); in this patients a good correlation between US and CT findings was noted(r = 0. 77, p<0.001). In majority of patients (71.4%) US detected alveoli-interstitial lesions; bronchiectasis were detected in only 2 cases by US, while CT revealed their presence in almost 90% of patients, showing a low US/CT correlation (r = 0.14, p<0.9). Pneumothorax was detected in 0.09% of patients. Lung ultrasound is a reliable method for detection of substantial lung alterations in children with CF; for lesions like bronchiectasis, CT remain superior. US could be use for rapid and safe evaluation in CF pulmonary exacerbations.