Sleep-related breathing disorders and pulmonary hypertension (PH) are inextricably linked, although the mechanisms of association are complex. Physiologic changes associated with sleep-related breathing disorders, including hypoxia, hypercoagulability, and systemic inflammation, may result in alterations in pulmonary hemodynamics. While sleep-disordered breathing in and of itself may not result in severe PH, it likely results in elevated pulmonary arterial pressures. Treatment of sleep-disordered breathing appears to improve pulmonary arterial pressures. Data are needed to determine if the treatment of sleep-disordered breathing will improve clinical outcomes of patients with PH.