Tonsillar hyperplasia causing obstructive sleep apneas in children is a well-defined clinical entity with nocturnal CO2 retention, retarded growth, and impaired physical and psychological status. Pulmonary hypertension, cor pulmonale, and ultimately, death may develop in a small number of these children. This syndrome may also develop in children with only moderately enlarged tonsils in association with neuromuscular hypothonia or anatomical defects. Anamnesis will readily detect the children at risk. The syndrome is cured completely by tonsillectomy. The CO2 retention disappears and length and weight growths are accelerated after surgery.