The most common treatment for sleep disordered breathing (SDB) is adenotonsillectomy (AT). Following AT, SDB resolves in most cases, and gains in cognitive and behavior scores are consistently reported, although persistent neuropsychological deficits or further declines also have been noted. This study presents results of the comprehensive 1-year follow-up neuropsychological examinations for children in the Washtenaw County Adenotonsillectomy Cohort I (95% return rate). After adjusting for normal developmental and practice-effect related changes in control children, significant improvements 1 year following AT were noted in polysomnography and sleepiness, as well as parental reports of behavior, although cognitive outcomes were mixed. Children undergoing AT with and without polysomnography-confirmed obstructive sleep apnea improved across a range of academic achievement measures, a measure of delayed visual recall, short-term attention/working memory, and executive functioning, along with parental ratings of behavior. On the other hand, measures of verbal abstraction ability, arithmetic calculations, visual and verbal learning, verbal delayed recall, sustained attention, and another measure of visual delayed recall demonstrated declines in ability, while other measures did not improve over time. These findings call into question the expectation that AT resolves most or all behavioral and cognitive difficulties in children with clinical, office-based diagnoses of SDB. (JINS, 2012, 18, 212–222)