Inclusion Criteria:

1. Ages 5.0 to 9.99 years at time of screening.
2. Diagnosed with Obstructive Sleep Apnea defined as: Obstructive Apnea Index (OAI) ≥ 1 or Apnea Hypopnea Index (AHI) ≥ 2, confirmed on nocturnal, laboratory-based PSG and Parental report of habitual snoring (on average occurring >3 nights per week).
3. Tonsillar hypertrophy ≥ 1 based on a standardized scale of 0-4: 0 = surgically absent, 1 = taking up < 25% of the airway, 2 = 25 - 50 % of the airway,3 = 50 - 75 % of the airway, 4 = > 75% of the airway
4. Deemed to be a surgical candidate for AT by ENT evaluation.

Exclusion Criteria:

1. Recurrent tonsillitis defined as: >3 episodes in each of 3 years, 5 episodes in each of 2 years, or 7 episodes in one year
2. Craniofacial anomalies, including cleft lip and palate or sub-mucosal cleft palate or any anatomic or systemic condition which would interfere with general anesthesia or removal of tonsils and adenoid tissue in the standard fashion
3. Obstructive breathing while awake that merits prompt AT in the opinion of the child's physician
4. Severe OSAS or significant hypoxemia requiring immediate AT as defined by: OAI>20 or AHI>30, desaturation defined as SaO2 <90% for more than 2% sleep time
5. Apnea hypopnea indices in the normal range (OAI < 1 and AHI <2)
6. Evidence of clinically significant cardiac arrhythmia on PSG: Non-sustained ventricular tachycardia Atrial fibrillation, Second degree AV block: Sustained bradycardia < 40 bpm (> 2 minutes, Sustained tachycardia > 140 bpm (> 2 minutes)
7. Extremely overweight defined as: body mass index > 2.99 age group and sex-z-score
8. Severe health problems that could be exacerbated by delayed treatment for OSAS Including: Doctor-diagnosed heart disease or cor pulmonale, history of Stage II Hypertension (HTN) defined as > 99% percentile plus 5 mmHg for either systolic or diastolic, based on the age, gender, and height and/or requiring medication, therapy for failure to thrive or short stature, psychiatric or behavioral disorders requiring or likely to require initiation of new medication, therapy, or other specific treatment. School aged children, parental report of excessive daytime sleepiness defined as unable to maintain wakefulness, at least three times per week, in routine activities in school or home, despite adequate opportunity to sleep.
9. Severe chronic health conditions that might hamper participation including: severe cardiopulmonary disorders, sickle cell anemia, poorly controlled asthma, epilepsy requiring medication, diabetes (type I or type II) requiring medication, conditions likely to preclude accurate polysomnography (e.g. severe uncontrolled pain),mental retardation or enrollment in a formal school Individual Educational Plan (IEP) and assigned to a self-contained classroom for all academic subjects, history of inability to complete cognitive testing and/or score on DAS II of ≤ 55, chronic infection or HIV
10. Known genetic, craniofacial, neurological or psychiatric conditions likely to affect the airway, cognition, or behavior
11. Current use of one or more of the following medications: ADHD,psychotropics, hypnotics,hypoglycemic agents or insulin,antihypertensives,growth hormone, anticonvulsants,anti-coagulants,daily oral corticosteroids, daily medications for pain
12. Previous upper airway surgery on the nose, pharynx or larynx, including tonsillectomy. Ear surgery and/or PE tubes are not exclusion criteria
13. Receives Continuous Positive Airway Pressure (CPAP) treatment
14. A parent or guardian who cannot accompany the child on the night of PSG
15. A family planning to move out of the area within the year
16. Female participants only: Parental report that child has reached menarche