The aim of this study was to investigate the relation of serum monocyte to serum HDL cholesterol ratio with obstructive sleep apnea syndrome (OSAS). A total of 336 patients who underwent polysomnography (PSG) were included in this study. The individuals with an apnea hypopnea index (AHI) <5/h were included in the study as controls while the patients with an AHI > 5 and excessive daytime sleepiness were included in the study as OSAS patients. OSAS patients were compared with the control group for serum monocyte count, high density lipoprotein (HDL) levels, and monocyte to HDL ratio (MHR). Mild, moderate and severe OSAS subgroups were compared for the same parameters. Additionally, correlations of serum monocyte count, HDL level and MHR with other PSG parameters were analyzed. The mean MHR of control and OSAS groups were 12.90±6.64 and 4.91±6.98, respectively, and the difference was statistically significant (p=0.041). Mean HDL level of the control group was 47.25±13.61mg/dL while it was 43.14±13.61mg/dL in OSAS group (p<0.001). Comparison of OSAS subgroups for MHR and HDL levels revealed statistically significant differences (p<0.001 and p=0.020, respectively). MHR was higher in OSAS patients compared to the controls. MHR may be a new, useful predictor for OSAS.