['Obstructive sleep apnea syndrome (OSAS) is an independent risk factor for the development of cardiovascular events and hypertension. The possible causes are oxygen desaturation due to hypopnea, increased cytokine levels and insulin resistance. All these risk factors also have a role in the progression of chronic kidney disease (CKD). The aim of this study was to determine the relationship between OSAS and the severity of CKD.', 'We retrospectively evaluated the medical records of 175 subjects who were admitted for the polysomnography study. OSAS was diagnosed by polysomnography if Apnea-Hypopnea Index (AHI) > 5 and glomerular filtration rate (GFR) was calculated with Cockcroft-Gault formula. According to AHI, individuals with AHI < 5 were recruited as group 1 (OSAS negative group), those with AHI = 5-15 group 2 (mild OSAS group), those with AHI = 15-30 group 3 (moderate OSAS group), and those with AHI > 30 group 4 (severe OSAS group).', 'Of the subjects, 117 (67%) were men, 58 (33%) were women and the mean age was 54.0 ± 12.1 years. There were 28 (14.3%), 18 (10.3%), 35 (20.0%) and 97 (55.4%) patients in groups 1, 2, 3 and 4 respectively. The prevalence of diabetes mellitus and hypertension and body mass index was significantly higher in severe OSAS group (P < 0.05). A significant decrease in GFR was detected when the severity of OSAS increased (group 1 = 50.0 ± 11.8, group 2 = 44.8 ± 15.9, group 3 = 40.8 ± 14.7, group 4 = 38.8 ± 16.0; P for trend < 0.001).'] Is obstructive sleep apnea syndrome related to the progression of chronic kidney disease?