Numerous studies have shown that obstructive sleep apnea syndrome (OSAS) is associated with an increased cardiovascular morbidity and mortality. Obstructive sleep apnea syndrome and cardiovascular disorders are frequent diseases. They share several risk factors such as age, gender, obesity, smoking, and alcohol. Therefore it is difficult to demonstrate that OSAS is a cardiovascular risk factor, independent of previously known factors. Recent epidemiological studies and trials, consistent with the results of previous studies, have demonstrated a strong association between OSAS and systemic hypertension. They also suggest that there is a possible cause-effect relation between OSAS and coronary artery disease or cardiac arrhythmias. Studies demonstrating that early recognition and treatment of OSAS may be effective in reducing these cardiovascular complications are still needed.