Objective: Although the presence of a systemic inflammatory response is known in obstructive sleep apnea syndrome (OSAS), there have not been adequate investigations on the association of such a response with the predominance of apneas either in rapid eye movement (REM) or in the non-REM (NREM) phase. In this study, we compared interleukin-23 (IL-23) concentrations, a marker of sys-temic inflammatory process, in individuals with sleep apnea syndrome, whose apneas where predominant in the REM or NREM phase.Methods: Fifty-four patients aged over 18 years who were diagnosed as having OSAS based on polysomnography were includ-ed in the study. The apnea-hypopnea index (AHI) was used to divide patients into groups of AHIREM>AHINREM and AHINREM>AHIREM. In the blood samples drawn from the patients, IL-23 concentrations were measured using enzyme-linked immunosorbent assay.Results: The study included patients with OSAS aged 28-65 years, of whom 29 were AHIREM>AHINREM and 25 were AHINREM>AHIREM. The AHIREM>AHINREM OSAS group had no sex-based variance (14 males, 15 females), but the AHINREM>AHIREM group was substantial-ly composed of males (21 males, 4 females). The average AHI of the AHINREM>AHIREM group (43.34±21.40) was significantly higher than in the AHIREM>AHINREM group (26.79±17.32). IL-23 concentrations were higher in patients with AHIREM>AHINREM sleep apnea (225.38±77.29) compared patients with AHINREM>AHIREM sleep apnea (183.68±78.49).Conclusion: In AHIREM>AHINREM sleep apnea, the systemic inflammatory response may be more dramatic. Taking the AHIREM val-ue into consideration along with the average AHI value seems to be important for treatment modalities.