Purpose <p>Obstructive sleep apnea syndrome (OSAS) affects a substantial portion of the adult population, and chronic inflammation plays a crucial role in its pathophysiology. This study aimed to investigate the effectiveness of blood parameters and inflammatory indices in predicting OSAS severity.</p> Methods <p>Patients diagnosed with OSAS who presented to our clinic between December 2009 and December 2024 were included in the study. OSAS severity was determined based on polysomnography results. Blood parameters obtained during hospitalization were recorded. The following hematological indices were calculated from blood parameters: neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), prognostic nutritional index(PNI), pan-immune-inflammation value (PIV), and hemoglobin, albumin, lymphocyte, and platelet (HALP) index. Moreover, the potential role of these hematological parameters and indices in determining OSAS severity was investigated.</p> Results <p>A total of 1009 patients were included in the study. Among them, 106 had simple snoring, 214 had mild OSAS, 224 had moderate OSAS, and 465 had severe OSAS. No significant association was observed between OSAS severity and blood parameters, including albumin level, hemoglobin level, leukocyte count, neutrophil count, lymphocyte count, and platelet count, delta neutrophil index (DNI) (p-values: 0.083, 0.483, 0.347, 0.555, 0.878, 0.220, 0.459, respectively). Additionally, no significant correlation was observed between OSAS severity and hematological inflammatory indices such as NLR, PLR, SII, PNI, PIV, and HALP Index (p-values: 0.919, 0.369, 0.701, 0.581, 0.397, 0.503, respectively).</p> Conclusion <p>Inflammatory processes play a role in the pathophysiology of OSAS; however, the present study revealed no relationship between OSAS severity and hematological inflammatory indices.</p>