This study was done to know the prevalence of arrhythmias in children with adenotonsillar hypertrophy. The study included 40 children, 26 males and 14 females attending Pediatric Clinic, Kasr El Ainy ; their ages ranged from 3-6 years. After exclusion of children suffering from any cardiorespiratory or renal diseases, the study showed the prevalence of arrhythmias among the studied cases was 22.5% There was significant association between the presence of arrhythmias and the grade of adenoid hypertrophy.