Aim: Obstructive sleep apnea syndrome (OSAS) is a prevalent disorder and is associated with increased cardiovascular morbidity and mortality. OSAS is independently related to the cardiovascular risk factors that comprise metabolic syndrome, atherosclerosis, acute coronary syndrome, and sudden death. The prevalence of metabolic syndrome is 30%-40% in the Turkish population. However, there are no data about the prevalence of metabolic syndrome (MS) in Turkish patients with OSAS. The aim of this study was to determine the prevalence of VIS in Turkish patients with OSAS and MS-related cardiovascular diseases.