Acute respiratory conditions are conditions which cause sudden deterioration of respiratory function, also known as dyspnea. Main diagnostic challenge is to determine the etiology of dyspnea. Standard methods include clinical examination, most importantly auscultation and radiologic procedures. Most commonly used is chest radiography. Computerized tomography is a method of highest accuracy, however due to numerous reasons like high radiation dosage or incapability of performing the procedure bedside it can hardly become the method of choice in acute respiratory failure. Lung ultrasound has shown to be highly sensitive and specific in differential diagnosis of the most frequent acute respiratory conditions. This method can be applied bedside, it can be used even outside of hospitals, the follow-up is easy and it does not expose patients to ionizing radiation. It had been considered until recently that lung ultrasound is of no clinical importance due to almost complete reflection of ultrasound waves against lung surface, which makes lung ultrasound examination impossible. However, Lichtenstein revealed that by examining pleura and joined artefacts key information for making a right diagnosis can be obtained. Based on his discoveries, he developed a diagnostic algorithm „BLUE protocol“ which showed great accuracy in detecting the correct cause of acute respiratory insufficiency in a significant number of cases. Many studies show that lung ultrasound is more sensitive and more specific in comparison to chest radiography what makes him a powerful tool in hands of an experienced clinician. Further research needs to be undertaken in order to fully use its potential.