Obstructive sleep apnea/hypopnea syndrome (OSAS) is still not widely diagnosed in children as its clinical signs are extremely variable. The diagnosis is based on recognition of the nocturnal and diurnal clinical symptoms of the syndrome, but above all on analysis of a sleep recording revealing abnormal respiratory phenomena. This recording makes it possible to determine an Apnea/Hypopnea Index (AHI) for each hour of sleep. The abnormality threshold is 1.5AHI/h for children and 5AHI/h for adults. The higher the index, the more severe the OSAS. The consequences of this syndrome are far from negligible, leading possibly to learning difficulties, mood problems, growth abnormalities and delayed neurocognitive development; it may even have an impact on metabolism. The orthodontist, as a health specialist frequently in contact with young patients, needs to be able to detect OSAS by launching a dialogue on the question of sleep so as to refer the patient to a specialist who can confirm the diagnosis. Through observation of the patient, it is possible to identify children at risk. Potential OSAS can then be prevented or cured by increasing the volume of the upper airways thanks to orthodontic treatment. Management of patients suffering from OSAS is multidisciplinary, under the direction of the sleep specialist.