Sleep-related breathing disorders include obstructive apnoea, central apnoea and sleep-related hypoventilation. These nocturnal events have the potential to increase pulmonary arterial pressure during sleep but also in the waking state. "Pure" obstructive sleep apnoea syndrome is responsible for a small increase in pulmonary arterial pressure whose clinical impact has not been demonstrated. By contrast, in obesity hypoventilation syndrome or overlap syndrome (association of COPD with obstructive sleep apnoea), nocturnal respiratory events contribute to the development of pulmonary hypertension, which is often severe. In the latter circumstances, treatment of sleep-related breathing disorders is essential in order to improve pulmonary haemodynamics.Patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension are at risk of developing sleep-related breathing disorders. Obstructive and central apnoea can be observed as well as a worsening of the ventilation perfusion mismatch during sleep. There should be a strong suspicion of sleep-related breathing disorders in such a patient population, however the precise indications for sleep studies and the type of recording remain to be specified. The diagnosis of obstructive sleep apnoea syndrome in patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension should encourage treatment with continuous positive airway pressure. The presence of isolated nocturnal hypoxemia should also prompt the initiation of long-term oxygen therapy. These treatments are likely to avoid worsening of pulmonary hypertension. However, it is prudent not to treat central apnoea and Cheynes-Stokes respiration with adaptive servo-ventilation in patients with chronic right heart failure because of a potential risk of serious adverse effects from such treatment.In this review we will consider the current knowledge of the consequences of sleep-related breathing disorders on pulmonary haemodynamics in patients with and without chronic respiratory disease (group 3 of the clinical classification of pulmonary hypertension) and the effect of treatments of respiratory events during sleep on pulmonary hypertension. The prevalence, consequences and therapeutic options of sleep-related breathing disorders in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension will also be discussed (groups 1 and 4 of the clinical classification of pulmonary hypertension, respectively).