Obstructive sleep apnoea syndrome in a child is characterized by prolonged episodes of obstructive hypopnoea and/or apnoea of upper airway leading to morbidity. The most common risk factor is adeno-tonsillar hypertrophy. Obstructive sleep apnoea syndrome diagnosis is based on clinical ENT evaluation and an instrumental approach, such as pulse oximetry or the gold standard overnight polysomnography. The aim is to establish, in a population of children with suspected obstructive sleep apnoea syndrome, the frequency of this disorder, the effect of adenotonsillectomy and the risk of post-operative complications. A total of 481 patients (297 male, 184 female) with suspected obstructive sleep apnoea syndrome (aged 2-14 years) were evaluated between March 2007 and April 2010 and divided into 3 morphological phenotypes: classic, adult and congenital. All patients underwent ENT assessment and a pulse oximetry with 4 channels cardiopulmonary monitoring. The examination following the Brouillette criteria was defined as negative, positive or inconclusive; when positive, adenotonsillectomy was the first therapeutic approach. At 6 months after surgery, all patients underwent check-up pulse oximetry. Of the overall sample, 96% of the patients had a classical phenotype, 3% an adult type and 1% a congenital type. The monitoring resulted pathological in 19% (17% of them were at increased post-operative risk), negative in 61% and inconclusive in 20%. All 5 patients with congenital phenotype were positive. Of the positive patients, 86% underwent adenotonsillectomy and a control pulse oximetry 6 months thereafter, 96% resulted negative. Pulse oximetry was efficient in order to avoid incorrect surgery indications, improving appropriateness and safety of adenotonsillectomy in children with obstructive sleep apnoea syndrome. Adenotonsillectomy showed a success rate of 96% and there were no episodes of post-surgery complications in particular in those patients at increased risk.