* Abbreviations: BIA — : Brief Intellectual Ability CHAT — : Childhood Adenotonsillectomy Trial NEPSY — : Developmental Neuropsychological Assessment OAHI — : Obstructive Apnea-Hypopnea Index OSA — : obstructive sleep apnea OSDB — : obstructive sleep-disordered breathing POSTA — : Preschool Obstructive Sleep Apnea Tonsillectomy Adenoidectomy RCT — : randomized controlled trial Adenotonsillectomy represents 15% of all surgical procedures in children <15 years of age.1,2 The primary indication for adenotonsillectomy has shifted over the last 20 years from recurrent throat infections to obstructive sleep-disordered breathing (OSDB) and obstructive sleep apnea (OSA).3 OSDB includes disorders ranging from primary snoring to OSA and can result in a significant negative impact on quality of life and other health-related consequences. Specifically, OSDB has been associated with a decrease in IQ, attention-deficit/hyperactivity disorder, emotional lability, enuresis, and learning impairment.4 Although the exact relationship between OSDB and neurocognitive deficit is unclear, 1 hypothesis is that respiratory disruptions lead to sleep fragmentation and episodic hypoxia, promoting systemic inflammatory changes and vascular changes in specific parts of the brain, resulting in impaired daytime functioning.5–7 Although disruptions sometimes result in excessive daytime somnolence (as in adults), in young children, it is more common to observe hyperactivity, impulsivity, and poor attention span.8–11 Some evidence exists that OSDB treatment may result in improvement in these sequelae12–14; however, little evidence on this subject addresses the preschool age group (3–5 years of age). The Preschool Obstructive Sleep Apnea Tonsillectomy … Address correspondence to David O. Francis, MD, MS, Division of Otolaryngology, Department of Surgery, University of Wisconsin–Madison, 600 Highland Ave, K4/7, Madison, WI 53794. E-mail:dofrancis{at}wisc.edu