The inflammatory process plays an important role in the development of cardiovascular complications in patients with obstructive sleep apnea syndrome (OSAS). YKL-40/chitinase 3-like protein 1 is a novel biomarker of systemic inflammation. This study aimed to investigate whether carotid intima-media thickness (CIMT), a useful marker for early atherosclerosis, is associated with serum YKL-40/chitinase 3-like protein 1 levels in patients with normotensive and nondiabetic OSAS.