The purpose of the study was to examine the effects of continuous positive airway pressure (CPAP) treatment on inflammation parameters in patients with obstructive sleep apnea syndrome (OSAS).Patients aged 18 to 65 years who underwent polysomnography (PSG) in the sleep clinic between January 1, 2019, and December 31, 2019, were included in the study. Patients with severe OSAS initiated treatment with CPAP. Patients and control subjects were assessed for levels of periostin, TNF-alpha, TGF-beta, and IL-6. Patients were re-evaluated 3 months later. Comparisons for the serum markers were made between controls and patients of different severity of OSAS. Comparisons of serum markers were also made between baseline and 3 month follow-up.  RESULTS: A total of 92 patients were enrolled in the study, including 25 controls (apnea-hypopnea index or AHI < 5/h), 39 patents with mild to moderate OSAS who did not receive CPAP, and 28 patients with severe OSAS receiving CPAP treatment. When all three groups were compared, levels of periostin, TNF-alpha, TGF-beta, and IL-6, as inflammatory markers, were higher in the OSAS group, though not at a statistically significant level. In patients with severe OSAS, there were statistically significant decreases in the TGF-beta 1, TNF-alpha, and IL-6 values between baseline values and the same measures taken after 3 months of CPAP treatment. Periostin values also decreased after treatment, but this decrease was not at a significant level.Inflammatory parameters of patients with OSAS were significantly higher compared with healthy participants. Regression of inflammation was detected after CPAP treatment.