Obstructive sleep apnea is the most common sleep-related breathing disorder. This is a relatively common, but insufficiently recognized medical problem associated with many chronic diseases such as hypertension, metabolic syndrome, diabetes etc. Airway obstruction during sleep leads to reduced or absent breathing which interferes with respiratory function and sleep quality. Symptoms include snoring, episodes of sleep apnea, daytime sleepiness, and fatigue. The biggest risk factors are older age, obesity and certain anatomical anomalies. Based on the medical history, evaluation by the available short questionnaires as a method of screening and clinical examination, the existence of sleep-related breathing disorders could be suspected, and the definitive diagnosis will be confirmed by the finding of all-night polysomnography. So far, the most common method of treatment is the application of continuous positive pressure on the airways (CPAP) through the nasal or oronasal mask. Patient adherence is the most important to achieve positive treatment effects. In milder cases, a change in lifestyle, primarily physical activity and weight loss, may be sufficient to improve symptoms. The long-term effects of hypoxemia and hypercapnia present in patients with sleep apnea lead to changes in the pulmonary vasculature and the development of pulmonary hypertension. It is estimated that about 20% of patients with obstructive sleep apnea also have pulmonary hypertension. The use of CPAP reduces pulmonary artery pressure and pulmonary vascular resistance and thus alleviates symptoms and improves the prognosis in patients with obstructive sleep apnea and pulmonary hypertension.