Sleep-disordered breathing in children has been associated with cognitive impairment. The purpose of this study was to examine the impact of tonsillectomy and adenoidectomy (T&A) on sleep, respiration and cognitive function in children of pre-school age with obstructive sleep apnoea (OSA) from a low-income community population.Altogether, 19 children attending state-funded pre-school programmes underwent overnight polysomnography and cognitive assessment before and following surgical treatment for OSA; 19 matched controls were also assessed.Following T&A, OSA subjects' delta sleep increased, rapid eye movement sleep decreased, and respiratory and arousal indices improved. There were no significant differences in OSA subjects' post-operative sleep or respiratory measures compared to controls. Prior to T&A, cognitive scores were significantly lower in OSA subjects versus controls; following T&A, OSA subjects' scores improved compared to pre-operative scores and did not differ from those of matched controls.Following tonsillectomy and adenoidectomy, at-risk pre-schoolers recruited directly from the community showed normalised sleep and respiratory patterns and improved cognitive scores. These findings, in this uniquely vulnerable population, which is unlikely to seek evaluation and treatment for obstructive sleep apnoea, underscore the potential value of outreach screening programmes for sleep-disordered breathing, particularly among low-income groups of pre-school age.