Aim: The aim of this study was to assess the insulin resistance and serum leptin levels in patients with obstructive sleep apnea syndrome (OSAS), and to compare body mass indexes (BMI) of OSAS patients with matched controls without OSAS. Method: Twenty eight patients having apnea-hypopnea index (AHI)≥5 included in the study. Thirty two healthy subjects assumed as a control group. Venous blood was obtained in the fasting state for the measurement of glucose, insulin and leptin levels. Insulin resistance index was based on the homeostasis model assesment method (HOMA-IR). Result: There was no significant difference in the serum leptin levels (control group, 32.88±24.22 ng/ml, OSAS group, 24.93±25.84 ng/ml) and HOMA-IR (control group, 3.01±1.81, OSAS group, 2.58±1.21) between control group and OSAS patients. Insulin resistance and circulating plasma leptin concentrations in OSAS patients were independent of the AHI and were not different from the control group. Conclusion: We concluded that insulin resistance and plasma leptin concentrations are mostly associated with the degree of obesity and BMI. Those parameters seem not to be related with the AHI in OSAS patients.