Aim of this study was to evaluate serum concentration of Pregnancy-Associated Placental Protein-A (PAPP-A) in obstructive sleep apnea syndrome (OSAS) and to examine the relationship of PAPP-A with disease severity and body mass index (BMI). 60 OSAS patients and 21 control subjects included. All study participants were evaluated with polysomnograpic data, BMI, serum lipid, insulin, glucose and PAPP-A levels.PAPP-A values were higher in OSAS group than control group. When the groups were examined according to apnea-hypopnea index (AHI), PAPP-A level of severe OSAS group was determined to be significantly higher than that of control and mild and moderate OSAS groups. As the severity of OSAS increased, the level of PAPP-A increased. In ROC analysis applied to PAPP-A levels of the OSAS and control groups, the optimum cut-off point for serum PAPP-A levels in this study population was 2.38 ng/ml. A positive correlation was determined between PAPP-A levels, BMI and insulin levels. PAPP-A could be a clinical marker for the risk of metabolic syndrome and cardiovascular events in OSAS. Since OSAS patients have a high risk of developing cardiovascular disease, it would be useful to assess prognostic data provided by PAPP-A.