Obstructive sleep apnoea syndrome (OSAS) is the most severe form of sleep-related disordered breathing (SRDB) and is characterised by snoring, apnoeas, and/or hypopnoeas associated to hypoxia, hypercarbia, or repeated arousals from sleep. OSAS has three major categories of morbidities: neurobehavioural, cardiovascular and somatic growth failure. The gold standard for objective diagnosis of obstructive-SRDB severity is polysomnography (PSG). The indication for surgical treatment in children is moderate-severe OSAS (AHI, apnoea hypopnoea index > 5/h) and in mild OSAS (AHI 2-5/h) with complications or morbidity. The entire spectrum of PSG-defined SRDB (ranging from Primary Snoring to severe OSAS) may correlate with behavioural, attentional and executive function deficits relating to hypoxia and sleep disruption: in some cases, these alterations may mimic attention deficit hyperactivity disorder (ADHD). The aim of this research was to evaluate visuoperceptual and constructional abilities, paediatric sleep questionnaire and polysomnographic scores before and 6 months after adenotonsillectomy with objective and subjective information. We included 59 children who underwent neuropsychiatric and otolaryngologist clinical evaluation and the Beery-Buktenica Developmental Test of Visual-Motor Integration (VMI); children parents were asked to fill in the Paediatric Sleep Questionnaire (PSQ); each child underwent PSG. At 6 months after adenotonsillectomy, all patients were evaluated again. There is a significant difference in PSQ parameters, VMI standard, visual tests scores and PSG parameters before and after adenotonsillectomy in children affected by OSAS. These results showed the achievement of therapeutic benefits with improvement of the quality of life for both children and their parents.