Introduction: Children with Down syndrome (DS) commonly have obstructive sleep apnea (OSA) though undervalued by parents and physicians. Several sleep questionnaires are used in paediatric patients to detect high risk children who have OSA, but not really appropriate for DS patients. The aim of the study is to determine the reliability of four questionnaires used in paediatric patients (PSQ-SRBD: Pediatric Sleep Questionnaire-Sleep-Related Breathing Disorder, CSHQ: Children's Sleep Habits Questionnaire, CAS-15: Clinical Assessment Score-15 and SCR: Sleep Clinical Record) in screening of OSA in DS population.