Current guidelines recommend AT as a first line treatment for pediatric OSAS even for those patients who may have significant risk of post-AT OSAS. Estimates of the prevalence of persistent OSAS after AT vary widely due to use of different polysomnographic criteria for diagnosis. Studies that assessed the risk of post-AT OSAS using a conservative adult threshold for diagnosis demonstrated that even with this high threshold at least 13-29% of children undergoing AT for pediatric OSAS will have significant residual disease and approximately 75% of children will fail to achieve normalization on polysomnography. Specific populations of patients that have been recognized to be particularly at risk for post-AT OSAS include those with severe baseline OSAS, Down syndrome, obesity, and age > 7 years. In obese patients, the prevalence of post-AT OSAS has been reported as high as 73-88%. Since obesity has tripled over the last three decades and now affects approximately 8% of children aged 2-5 years, 18% of children aged 6-11 and 21% of adolescents aged 12-19 years, the problem of persistent OSAS after AT is likely to continue to grow.