Obstructive sleep apnea syndrome (OSAS) was first reported in 1976 by Guilleminault. This condition has been defined as a disorder of breathing during sleep characterized by prolonged partial/complete upper airway obstruction that disrupts normal ventilation and normal sleep patterns. The prevalence of this condition varies among the different populations but it is between 1 and 2% in preschool children when adenoid and tonsils volume has a major peak. Loud snoring is very common in these children but not always present. The diagnosis may be suggested by the facial appearance and by personal history but it must be confirmed by a polysomnography recording. OSAS has many associated morbidities which involve the cardiovascular system, the neurocognitive performance, the growth and the metabolic homeostasis. Obesity is a common associated condition and it impairs the therapeutic success. It should be considered when planning the treatment program: it should be stressed the obesity epidemic has already reached the European countries and it is now contributing to the "adult type" of OSAS which was quite rare in childhood until few years ago. The adenotonsillectomy is the most common therapeutic intervention but it is curative only in 2/3 of patients. Orthodontic approaches, associated with orofacial muscle reinforcing physiotherapy are helpful in most of these patients. To conclude we must stress that this condition is quite common and should be promptly diagnosed to prevent the multisystem morbidities; a multidisciplinary approach should be always offered to the parents of these children.