The obstructive sleep apnea syndrome (OSAS) is associated with the development/worsening of cardiovascular disease. OSAS is considered to be an independent risk factor for hypertension and is linked to increased mortality in the context of coronary heart disease, the development of cardiac arrhythmias and increased risk of developing mild pulmonary hypertension. OSAS is also associated with cerebrovascular mortality and morbidity. In heart failure, OSAS can lead to worsening of symptoms. Treatment of OSAS using positive airways pressure therapy (PAP) has been shown in randomized, controlled trials in selected populations to reduce some, but not all of these cardiovascular and cerebrovascular risks. Unequivocal evidence of causality for OSAS in the development, progression, and outcomes of these disorders in all individuals suffering from them, is lacking. Good quality long-term morbidity and mortality data for the effects of OSAS on cardiometabolic health and the impact of PAP treatment are likewise limited.