Background: Evidence suggests that increased leukotriene level and receptor protein expression emerged in the adenotonsillar tissue of children with sleep-disordered breathing (SDB). Nevertheless, few studies have investigated the contribution of disease severity in the cysteinyl leukotriene (CysLT) production and cysteinyl leukotriene receptor (CysLTR) expression. Furthermore, the relationship between local upper-airway and systemic inflammatory responses remains undefined. Methods: A prospective, observational study that included standard questionnaires, physical examinations and overnight polysomnography. CysLTs were determined from serum, urine and tonsillar homogenate supernatant by means of enzyme-linked immunosorbent assays. The protein expressions of CysLTR were measured using Western blot analysis. Results: Children with SDB had increased intratonsillar CysLT levels as well as CysLT subtype 1 receptor (CysLT1-R) and CysLT subtype 2 receptor (CysLT2-R) protein expression than the control group. CysLT concentration was positively correlated with body mass index z-score and apnea-hypopnea index (r=0.454 and 0.487, p<0.001 respectively), and negatively correlated with pulse oximetric saturation nadir (r=-0.518, p<0.001). Upper-airway intratonsillar CysLT production was positively correlated with systemic production (vs. urinary LTE4: r=0.456, p<0.001; vs. serum CysLTs: r=0.440, p<0.001). Immunoblots showed that CysLT1-R protein expressions were modestly higher in the severe group when compared to the mild group. In contrast, there were no differences in CysLT2-R protein appearing among the SDB subgroups. Conclusions: Increased CysLT level and receptor expression in upper-airway tonsillar tissues are related to disease severity in SDB children. The local and systemic CysLT production were positively correlated. (C) 2012 Elsevier B.V. All rights reserved.