Introduction: Current evidence supports an association between Obstructive Sleep Apnea Syndrome (OSAS) and insulin resistance and type 2 diabetes mellitus (DM 2). The relation between glycemic profile and severity of OSAS, in nondiabetic patients, is complex and still remains poorly understood. Aim: To examine the potential correlation between sleep characteristics and glucose metabolism in nondiabetic patients, with OSAS. Materials and Methods: Included were one hundred and fifty seven (157, 104 men and 53 women), with mean age 46.63±10.45years old and mean Body Mass Index (BMI) 31.47±5.8kg/m 2 , nondiabetic patients, recently diagnosed with OSAS, by full polysomnography. Patients were subdivided into four groups, according to their fasting plasma glucose (FPG) levels: group I: ≤75mg/dl (n=44), group II: 76-86mg/dl (n=37), group III: 87-96mg/dl (n=33) and group IV: ≥97mg/dl (n=43). Results: Both, group I, with the lowest FPG and group IV, with the highest FPG were strongly associated with apnea-hypopnea index (AHI) (p=0.02), a widely accepted marker of the severity of OSAS, and with percentage of sleep time with saturation of hemoglobin with oxygen as measured by pulse oximetry (SpO2) < 90% (t < 90%), (p=0.041). Conclusions:In conclusion, the severity of OSAS among nondiabetic patients correlates in a u-shaped relation with FPG. A compensatory, early rise in insulin secretion to maintain normal to low FPG could be an underlying mechanism that promotes the future development of DM 2, in OSAS. More studies are needed to assess whether early diagnosis and treatment of OSAS may reverse insulin resistance and prevent progress to diabetes.