Even within populations at risk for AT failure, there is a wide variation in treatment response. One study of morbidly obese children undergoing AT demonstrated only a 37% cure rate while 53% had sufficient residual OSAS to require further treatment with continuous positive airway pressure (CPAP). However, no significant baseline differences were identified between surgical responders and non-responders. The mechanism for failure in this population is unclear, but it is presumed that increased generalized adiposity leads to multilevel obstruction similar to obese adults, thus decreasing the likelihood of success with AT. Similarly a poor but still variable response to AT was observed in children with Down syndrome with post-AT success varying between 18% and 55% depending on the specific criteria used. There are no studies that have clearly identified predictors of AT outcome within the Down syndrome population, however, some studies of Down syndrome patients who failed AT have suggested that multilevel obstruction is common. Thus, although specific populations of patients are known to have greater risk of post-AT OSAS on average, the individual characteristics causing persistent disease remain unclear. Accurate prognostication of the risk of residual OSA after AT for any individual patient remains a challenge. Studies of patients with persistent post-AT OSAS have suggested that multilevel obstruction at locations besides the tonsils or adenoids are likely contributors, but this has not been clearly demonstrated. In this study, we present a novel concept for building a composite model to predict the outcome of AT in children with OSAS. This model will include not just baseline features of history and physical exam but also the findings of dynamic sleep-related collapse at specific anatomic sites in the pharynx observed during sleep endoscopy. This model will give further insight into the mechanisms of airway obstruction as well as the possible reasons for persistent OSAS after AT.