The obstructive sleep apnoea syndrome (OSAS) in children is a clinical syndrome resulting from complete or partial obstruction of the upper respiratory tract during sleep. The pathogenesis is multifactorial; clear risk groups are children with anatomical anomalies of the upper airways, neurological abnormalities and genetic syndromes (including craniofacial syndromes). The clinical symptoms of OSAS in children vary. In partial obstructions, the most frequent forms, the patients may snore and have impaired respiration during sleep. Polysomnography contributes to definite confirmation and specification of the clinical diagnosis. Standard values should be interpreted with respect to age. Adenotonsillectomy is the most frequent treatment of children with OSAS. In persistent symptoms, continuous positive pressure therapy is often successful. The natural evolution and the long-term prognosis of OSAS in children are still unknown.