Non-invasive mechanical ventilation (NIV) is a form of mechanical ventilatory support. It is most often used in the treatment of acute respiratory insufficiency, but the greatest benefit of this form of respiratory support has been shown in the acute exacerbation of chronic obstructive pulmonary disease (COPD) with consequent global respiratory insufficiency. In patients with worsening COPD, non-invasive ventilation therapy has been shown to significantly reduce CO2 partial pressure, increase blood pH, reduce breathing frequency and reduce shortness of breath. The research deals with the use of non-invasive ventilation (NIV) in patients with chronic obstructive pulmonary disease (COPD) and pneumonia. Application of NIV reduces breathing frequency and transdiaphragmatic activity with consequent increase in respiratory volume and minute ventilation. Therefore, this form of respiratory support has a favorable effect on the mechanics of breathing and reduces the work of breathing, which enables the recovery of the respiratory musculature, reduces the degree of shortness of breath and the frequency of breathing. NIV improves respiratory gas exchange resulting in prompt improvement of oxygenation, reduction of partial pressure of carbon dioxide in arterial blood (PaCO2) with improvement of pH. One of the reasons for the increasing use of NIV in the management of COPD is to avoid the complications of invasive mechanical ventilation, especially pneumonia associated with mechanical ventilation. NIV is a way to support breathing through positive pressures using various interfaces and without the need to use endotracheal tubes. These interfaces can be: a mask over the patient's nose, a mask over the patient's mouth and nose, a mask over the entire face of the patient or a helmet. The results of the survey revealed that the most common medical diagnoses for NIV use were pneumonia and COPD, with combinations of these diseases often occurring. Elderly patients (> 60 years old) were on average NIV V60 for three to five days, while younger patients usually spent less than two days on this therapy. The research results, based on the medical documentation of the Rijeka Clinical Hospital Center, lead to the conclusion that NIV is an important form of therapy for patients with COPD and for patients with pneumonia. The use of NIV in more than 76% of cases ended with the improvement of the patient's health condition.