Background: The obstructive sleep apnea syndrome ( OSAS) is closely associated with cardiovascular and metabolic disorders. Objectives: The aim of this study was to evaluate the influence of OSAS on plasma adiponectin levels independent of obesity in our study group. We also investigated the association between plasma adiponectin, plasma tumor necrosis factor-alpha (TNF-alpha), obesity, cardiovascular disease (CVD) and OSAS. Methods: The patients were classified into controls or OSAS patients according to the apnea-hypopnea index (AHI): patients with an AHI ! 5 constituted the control group (n = 32) and patients with an AHI 6 5 constituted the OSAS group ( n = 106). Plasma TNF-alpha and adiponectin levels were measured in both groups. Results: Plasma adiponectin levels were negatively correlated with AHI, body mass index (BMI) and SpO(2) <90% and positively correlated with minimum oxygen saturation. The plasma levels of TNF-alpha were positively correlated with SpO(2) <90%, BMI and fasting plasma glucose levels. In addition, there was a significant negative correlation between plasma TNF-alpha and adiponectin levels in the OSAS group. Compared with the non-obese OSAS group, subjects with obesity and OSAS had lower adiponectin levels and SpO(2) <90%, and higher TNF-alpha levels. Obese OSAS patients had higher rates of CVD with lower plasma adiponectin levels when compared with obese control subjects. Conclusion: Serum adiponectin is significantly lower in patients with OSAS and it is independent of obesity. This might explain the high incidence of CVD and metabolic syndrome in patients with OSAS. Copyright (C) 2008 S. Karger AG, Basel.