Adenotonsillectomy is first-line treatment for pediatric obstructive sleep apnea syndrome (OSAS) when not otherwise contraindicated. There is concern severe OSAS increases risk of comorbid cardiopulmonary abnormalities, such as ventricular hypertrophy or pulmonary hypertension, which preoperative testing could detect. Our objective is to determine if there is a severity of pediatric OSAS where previously undetected cardiopulmonary comorbidities are likely.