Aim. We aimed to investigate the relationship between serum pregnancy-associated plasma protein A (PAPP-A) levels and obstructive sleep apnea syndrome (OSAS). Materials and Method. 44 patients with OSAS and 44 healthy adults were included in this study. The participants having rheumatic or systemic inflammatory disease, advanced liver or kidney failure, diabetes, heart failure, hypertension, pregnancy, prerenal azotemia, known history of coronary artery disease, any pulmonary disease, rhinitis, or atopy, history of major trauma or surgery within the last six 6 months, and inhaled nasal or systemic corticosteroid use or other anti-inflammatory medications and those with <18 years of age were excluded. Serum PAPP-A levels were determined by the Elisa method with the immune sandwich measuring method. Statistical analysis of the study was performed with SPSS 17.0 statistical analysis package program, and p<0.05 was considered as significant. Results. Serum PAPP-A levels of patients with OSAS (2.350 ng/ml (0.641–4.796)) were significantly higher (p<0.001) when compared with healthy controls (0.971 ng/ml (0.109–2.679)). There was a statistically significant difference in serum PAPP-A levels between groups of OSAS patients according to the classification of OSAS severity. Between the groups of patients with OSAS, serum levels of PAPP-A in moderate group was significantly higher when compared with severe OSAS group (p<0.001). There was positive correlations between PAPP-A levels and night minimum (p=0.042,  r=0.309), and average oxygen levels (p=0.006,  r=0.407). There was a negative correlation between PAPP-A levels and AHI (p=0.002,  r=−0.460). Conclusion. Higher PAPP-A levels in OSAS patients that were found in this study show inflammatory component in OSAS.