In three children aged 3, 9 and 10 years the syndrome of sleep apnea with typical manifestations of obstructive apnoeic episodes during sleep is described. In two instances the nocturnal periodic apnoeic spells were associated with marked varying hypoxemia, objectively recorded by continuous monitoring of the transcutaneous oxygen tension using a skin oximeter. In one child the cause of airway obstruction during sleep were hypertrophic tonsils and adenoid vegetation, in the other two children in the nocturnal apnoeic spells above all the functional component participated, expressed by increased relaxation of the oropharyngeal musculature during sleep. In the first child adenotonsillectomy was followed by immediate regression of all original symptoms, in the remaining two children therapeutic results were achieved only by removal of the slightly enlarged tonsils, while previous adenotomy did not have a favourable effect on the course of their disturbed sleep. Permanent regression of the apnoeic episodes after tonsillectomy was confirmed by records of a smooth level of the skin oxygen tension during sleep. This syndrome is more frequent than generally assumed and late establishment of the diagnosis may lead to the development of serious cardiopulmonary complications, irreversible neurogenic dysfunctions and psychosomatic retardation of the affected children.