The objective of this article is to review the available data on the relationship between sleep-disordered breathing (SDB) and pulmonary arterial hypertension (PAH), with a focus on the prevalence of SDB in patients with idiopathic PAH (IPAH); the prevalence of PAH in patients with SDB; and the effects of SDB treatment on PAH. The evidence to date suggests that PAH may occur in the setting of SDB, although the prevalence is low. However, pulmonary hypertension (PH) in SDB is most strongly associated with other risk factors, such as left-sided heart disease, parenchymal lung disease, nocturnal desaturation, and obesity. The limited data available also suggest that SDB is uncommon in patients with IPAH. Treatment of SDB with continuous positive airway pressure may lower pulmonary artery pressures when the degree of PH is mild.