Objective: Obstructive Sleep Apnea syndrome (OSAS) is the most common condition among sleep-related respiratory disorders. The etiology is not clear. However, systemic and local inflammation in the respiratory tract of the patients has been acknowledged. Monocytes and macrophages play the critical role in the inflammation process. These cells participate in the release of the proinflammatory cytokines in inflammation sites. High-density lipoprotein (HDL) cholesterol is a molecule with an anti-inflammatory effect. Monocyte/HDL cholesterol ratio (MHR) is an inflammation marker being used recently. In our study, we aimed to compare inflammation marker levels between patients diagnosed with OSAS with subsequent polysomnography and the non-OSAS group, determine the relationship between the severity of OSAS and MHR and, investigate the utility of the MHR for diagnosing OSAS.